It is ironic, yet sensible in a way, that even though our lives are limited in duration, it is encouraged and even desired to limit them even further, whether it is by using life-shortening substances such as smoking and fast food, or through non-damaging ways such as watching television and playing games.
However, regardless of whether you'll die sooner or later than expected, many of us find ourselves with nothing to do sometimes, so we are "confined", allegedly, to kill our free time and thus, bring us "closer" to death (even though killing time does not decrease the length of your lifetime, of course).
Why do we kill time, then, if our lives are limited in duration and thus, our opportunities are not permanent in availability as well? Why is it considered "good" or even "awesome" to spend the whole weekend watching television when that weekend could have been used for other, more productive activities? It is not, of course, to criticize one's ways of leisure, but to simply raise this question -- why limit our output of productivity, when we can increase it, especially given the fact that some of us actually look to be more productive in their own individualist ways?
Here are some possible answers to your question:
We may be afraid of death.
The fact that our lives are limited in duration can be a scary thought. It can make us feel like we don't have enough time to do everything we want to do, or that we're going to miss out on something important. This fear can lead us to make choices that we think will help us to live longer, even if those choices are not actually in our best interests.
We may be stressed out.
Modern life can be very stressful. We have a lot of demands on our time, and we often feel like we're not doing enough. This stress can lead us to seek out activities that help us to relax and de-stress, even if those activities are not productive.
We may be bored.
Sometimes, we just don't know what to do with our free time. We may have exhausted all of our options, or we may not be interested in anything that is productive. This boredom can lead us to engage in activities that are not productive, simply because they're something to do.
We may be trying to escape.
Sometimes, we use non-productive activities as a way to escape from our problems. We may be unhappy with our lives, or we may be dealing with difficult emotions. Engaging in non-productive activities can help us to forget about our problems for a little while, even if it's not a healthy way to deal with them.
It's important to find a balance between productive and non-productive activities. We need to make time for things that are important to us, but we also need to make time for things that help us to relax and de-stress. If we're constantly working and never taking any time for ourselves, we're not going to be very happy or productive in the long run.
I too enjoy watching TV and ordering fast food every now and then, but whenever I do that, I realize that the time I'm using could have been used otherwise, to bring me more satisfaction overall. Hence why I do it in moderation, because I know there is still more that can be done, especially the more I kill time, because when I kill time, I realize that this time will not come back.
Do you know what speedruns are in gaming?
Speedruns are basically the attempt to complete a game as quickly as possible, with as little time to waste as possible. I don't pretend to make my own life a "speedrun," but whenever I watch them I realize how little time could have been dedicated to be accomplish something very productively.
In other words, after watching some speedruns of games I used to play as a child, I realize how much time I "wasted" just to complete a game, when I have proof that they could have been completed after much, much less time. The same can be compared to whatever our ambitions are in our lives -- time is ticking, and it is more valuable than many of us may think, because of how productive time can be used as a resource to accomplish whatever we want or need to complete.
And still, many of us would choose the "Homer Simpson" route to life; you know, the one that lives life hedonistically with little accomplishment, even though much of our available time can be dedicated for just that. Additionally, unlike Homer, you won't get to have the same age for decades, because you'll eventually grow old and die, hopefully not prematurely. You may even procrastinate and put your ambitions far into the future, without actually knowing for sure if you'll manage to accomplish them.
What made me produce so much content over a relatively short length of time is the fact that I had enough with wasting too much time over things that give me and others little benefit. My entire childhood was just that -- having the time of my life playing games that gave me little benefit beyond the gratification of entertainment.
This eventually led me to be slightly against the concept of hedonism, because the fact that you enjoy from something right now does not mean you will not get to live and regret your lack of actual productivity and accomplishment as a distinct individual with distinct potential. This also led me to live a significantly more ascetic life, because hedonism taught me that fun alone is insufficient for a life well lived. There is a need for further substance, of depth, in order for the fulfilled individual to be truly fulfilled.
Writing so much, I basically "speedrunned" my life from teenage-hood to adulthood, with a productivity that equals to that of a far-older writer. This is not an expression of self-glorification, but simply a presentation of how you too can become more productive by leaving the TV, leaving the alcohol and nightclubs and actually use your given, limited time for becoming more productive. It doesn't matter whether you "only live once" or get to have multiple lives by having a soul.
You are not only given this life, but also a certain number of resources, skills, and perhaps even manpower. If we indeed live multiple lives, the attributes of our current lives will not be carried with us to the next, as they will stay here after we're dead. We should thus use them wisely, as they won't be within our possession forever, even if they themselves will remain for generations—like a corporation, a domain, or even a country, or at least some extra money that can be used to further push your endeavors to the next level.
In the end, some people are content with their lives as they are, even if they weren't as productive as they could have been. However, regardless of our age, I think we should put ourselves in the shoes of our own in the last days of our lives, and contemplate to ourselves whether or not we have done the things we truly wanted to do, and whether or not we have done them the way we wanted them to, even if confined to circumstance.
Finally, a fun fact -- according to this site, around 150 thousand people die every day, and around 6000 people die every hour. The average person rarely knows more than 6000 people, but each of their death is not only their own death, but the death of a potential; a potential that could've been used otherwise, for the better and for the worse. Always remember that everyone has their own hour, waiting for them, regardless if what they have done and haven't done. The bus will not wait not for the extremely lazy nor for the extremely productive.