Why do modern games automatically assume that multiplayer is what we want?

popularity and money says different,   and if i'm a games developer i would find it hard to argue with either,  besides there are still plenty of games which are single player or even single player only..but as far as FPS games go  human enemies can be way smarter and far less predictible that an AI enemy is,  although that is changing....and most gamers don't want repetive predictable actions,  they want diverse unpredictability and challenge, and humans are far more challenging.....i'm not going to guess why you're complaining like this, but i can guess already,  my advice practice, don't take it so seriously, or play something else

Playing Outriders, huh? You can set the default to closed in the settings.

Games like GTA Online and Fortnite and Minecraft have been making way more money then they ever expected, they've been breaking records making money, and other companies are taking notice and want some of that money too. So a lot of developers are focusing most of their efforts on online features and micro dlcs. For example, the upcoming batman and suicide squad games have announced they're going to be full online live service games. I agree with you, I dont like it either. You have to do research into the games you buy to make sure its not an online heavy game nowadays and that sucks.