its the natural end of video games. games are only fun when you have the opportunity to learn new patterns and how to solve them. once you solve and understand a pattern the only fun way to tackle it again is with added constraints like time attacks or multiple patterns at once. however eventually you find the optimal way to solve that too and then your brain can no longer have fun solving that pattern again.
the problem is that most video games are built on the same inspiration- they share similar gameplay, similar patterns and mechanics. therefore when you beat call of duty for the first time, beating the next call of duty won't be as fun or fulfilling as the first. after your nth shooter, your brain understands every mechanical detail and therefore exploring it is no longer fun. same with platformers, strategy games, rhythm games, mobas, and everything in between. shooting your 200000th enemy with a shotgun isn't as fun as shooting your first enemy, because now you've explored the shotgun's cone meta 200000 times
the future of video games hangs in the development of unique mechanics and gameplay. it primarily hangs in new ways to explore familiar spaces. a good example of this is rocket league, a game where the normal constraints of gravity and 3d space are overcome with car control and rocket mechanics. another good example is papers please, an unusual pattern recognition game that allows you to explore the 2d space of your ticketing booth. games like this that introduce new ways to explore typical spaces are the only games that can be considered remotely fun to the brain of a veteran gamer
the other solution is mods and the capacity for enjoyment is determined solely by how much creative content the playerbase can generate. or if you're smarter than most people, making your own games is one way to find some enjoyment out of video games in general. once you've reached that point the fun in video games is no longer playing and understanding them, but watching other people play and understand them instead. eventually you stop watching people stream video games and instead watch people break down the mechanics of that video game, because understanding how good game mechanics work with each other is important information for your video game design conquest. Raph Koster coined a term for this called designeritis