Strictly speaking a lot of that was never supposed to be solely on the GMs plate to begin with, and its a weird self perpetuating aspect of the hobby that even people who absolutely hate it will turn around and say "yeah, only one person needs to actually know how to play the game".
There's also just a lot of preemptive infantilizing in that, a cynical assumption that people won't learn to play without a GM there to hold their hand.
Edit: I'll also say a big part of the issue is that the GM is all too commonly not treated as an equal player, and sometimes not even as a player at all, both culturally and in the design of many games. Its why so many resist doing it and a big reason why this culture self perpetuates, and most anybody has figured to do to address it is to just chase minimalism ad absurdum, which in turn often leads to just eliminating the role outright.
Though to be fair, I arrived there myself from the opposite approach, but thats only because I chased the fun, as the player experience in Labyrinthian proved to just be too enticing, and going for solo/coop will likely pay dividends for getting people to break from the weird mindsets they keep trying to come at the game with.
