A number of years ago I completed an MMO project by myself (art, programming, marketing, etc). It was fun! Real-time server was in Python Twisted, lots of Cython to speed up the deepest parts of the game loop. Django for the main website. The client was Flash (this was back in 2013, when it was still kinda a thing), which meant anyone could jump in really quickly, but technically that was challenging for a real-time…
I recently had some time off and ended up burning through nearly all of Destiny 2's content inside of 2-3 weeks. Hell, I can jump into WoW and be raid ready inside of a week or two, and just go straight into the latest raid. I think there's something fundamentally very wrong with how modern MMOS are designed, but it doesn't seem like anybody is interested in properly exploring the solution space.