You keep posting as if the only reason the GM would be subject to rules any stricter than introduce whatever fiction you think is worth introducing and that the other participants will accept would be because the GM is terrible and can't be trusted.Are the rest of us not playing a game? What you're saying here makes no sense to me.
Whereas the actual reason seems obvious to me: I want to play a game different from the one described in the previous paragraph - which gives the GM essentially unlimited authorial power - and hence I adopt different rules.