Gaming

I feel it's less of a cop-out and more of a matter of economy and the current state of video games.

The thing with game development is that the visuals always take the most resources and therefore the most effort (concept art, sculpting, retopology, modeling, texturing, rigging, animating, materials, particles, environment art).

You hit the nail on the head when you say that multiplayer is content that creates itself, and compared to singleplayer games for the same amount of "content/entertainment", it does require exponentially less work in visuals and just a tiny bit more in engineering. In a singleplayer game, once you beat a level, you're basically never seeing that map and all the love poured into it ever again. Replayability adds value to the visuals in a game, and what adds more replayability than multiplayer?

And that sort of transitions into the state of video games now, where these multiplayer games allocate all those extra development resources into the maintenance and expansion of the game by adding new seasons and firearms and skins and maps every few months, all to keep their playerbase playing and raking in the microtransaction revenue. It just makes economical sense to focus on the multiplayer.