This is a hot take (maybe) on my part, but if a person is going so far as to invite other people into a world/universe/lore they've crafted by way of making and RP, they've already handed away a noticeable degree of control to others anyways. From the point that a GM accepts another player's character(s) into the fold, absolute control is forefeited. And if a GM is too bogged down to give their own work any attention, but has half a dozen players that are able to willing to keep things going, seems a bit selfish to just pull the plug. What's the harm in having a Co-GM or two that can hold the fort while the GM Prime is busy with other life things?
If someone wants a story to move entirely at their discretion, they're best off just writing a solo piece, IMO.
Incidentally, I've personally seen more GMs with [mostly] original RPs willingly and smoothly hand the GM role to others than I have GMs running Fandom RPs. Both instances I cited of GMs denying or being less-than-amicable about transfer of responsibility were Fandom RPs, for example.
Maybe make your own RP at that point, then.
