Because video games are fun.
Thanks for reading.
...Alright, I'll go deeper. Video games have a hidden cost: your time. What you get in exchange for your time is fun, relaxation, a sense of accomplishment, maybe some new friends, or a chance to connect with your existing friends. That's why gamers tend to skew younger. Kids and young adults have time on their hands, a desire for community, and to feel accomplished.
Eventually, a lot of gamers "grow up" and stop playing games so frequently. Up through college, I logged hundreds of hours on Mario, Halo, WoW, Diablo, Hearthstone, etc. At college, I made friends who enjoyed tabletop games including D&D and MTG, so I got into those too.
When I got married and graduated, I stopped playing so many games. I had a job and spent most of my leisure time with my spouse. My time was at a premium and I chose to spend it on the things most important to me. I still have a sizable collection of games and I enjoy sharing them with my wife and kids, but I don't have anywhere near the amount of time for it as I used to.
What I do have now is money, and I'll happily spend some of it on a good game. The problem is that (at least for me) I no longer get the same sense of accomplishment from games. I could have spent my time and money on something more meaningful and long lasting.
Blockchain fixes this for games. If you can earn NFTs and cryptocurrencies by playing, that allows you to really own the results of your time/money investment. It may or may not be worth much monetarily, but the psychological impact is enormous. I believe this is the missing piece for a certain group of gamers like me. If you can spend your leisure time on a fun game and walk away with an asset that can be impactful in the other areas of your life, that's highly appealing.
Crypto shouldn't be the only reason you play, but it sure helps.
P.S. My theory is that as play-to-earn games become more mainstream, the average age of gamers will skew older.