Retro games are easy to acquire and you can have hundreds or thousands of them, and all those games take up less space than one modern game, especially when talking about retro games made before optical disks. Also, since there are hundreds or thousands of retro games, you are sure to find something to play, as opposed to that one modern game that you found you didn't like, or got tired of playing. Even if you only play one round on a retro game, since you have hundreds or thousands of them, you still have games for days.
For example, I have one of those multi-cade arcade machines that came with 300 built-in games (AtGames Legends Ultimate, or ALU), but I also added literally thousands more retro games to it. Everything from retro arcade games to legacy console emulation to old computer systems. I've been playing on that more than my PS5 for the last couple weeks. Games. For. Days. And besides the price of the cab and a couple flashdrives, those thousands of added games cost nothing but a little time to gather. And I've only used 2 of the 3 popular methods of adding games to it, so I could still add more.
Is it any wonder, in these overly expensive times we are living in, that people are getting into cheaper alternatives for gaming? Retro gaming is a game hoarder's treasure trove, it costs MUCH less and you get MUCH more for your HDD space than modern games could ever provide.