I think that online multiplayer games does not need to exist as most games could be played offline with AI and with higher enjoyment also.
I think the reason a lot of people don’t enjoy AI offline instead of multiplayer games is because as a capitalist society we associate multiplayer games with higher joy, due to the huge amount of ads and streamers targeting teenagers to show them how much fun they are missing by not playing in online multiplayer games. I had met a variety of people with different ages and a lot of the older generations prefer offline games and consider it the norm.
Finally, an opinion with more downvotes than upvotes.
But on a serious note, I think there is something to it when you know you play with/against real people - a sense of connection, a spirit of honest competition (not with a machine that is either poorly programmed or straight up let you win so you would feel better, like, good luck playing any board game against actually fully equipped AI), and then, chatting and social behavior.
This is why people get so pissed off when they see bots introduced into multiplayer games - all of a sudden, you can now never know if that juicy frag you made was against a real person you outcompeted or it was just AI that intentionally played dumb, being nothing but a dummy. There is also less connection and communication in that scenario.
There are also other cases like companies of friends playing together (co-op games exist, but are limited in scope and amount of players), or MMOs where entire economy and systems are built around players making the game and forming lively communities, roleplay, working together and waging wars, etc.