So the answer to "why do we distrust players but trust GMs" is "because we do."
Now you know why I have said the answers are unsatisfactory.
Note that presuming good faith on the GM's part but not presuming good faith on the player's part is specifically my issue here.
You as a player find a DM suitable to your roleplaying style. 1 Person.
As GM you have to find many players who are suitable to your playstyle. 1+ Person/s.
It is why many RPG advice books speak to the various types of RPG players personalities as opposed to the many GMs that exist.
Perhaps that is a fault of the PHB.
If you have a player amongst your group that
unwittingly dominates the table, pushes on power...etc, it is the GM's responsibility to handle that.
That responsibility can be given to the table and should (I believe) where possible.
And for the record, I'm not even talking about a bad player. I'm not even in that territory. I have such a player and he is enthusiastic as anything, he contributes, he is proactive, he is a great resource for me for the rules and bouncing ideas for homebrew material...etc
We often joke that the party is not him and company.
As a GM of D&D one manages players' playstyle preferences, manages characters' screen time, manage PCs' desires, manage PCs' and party storylines, manages setting data...etc
And GMs are not perfect. And a player (and table) has every right to check the GM in case a mistake has been made or an oversight has occurred. In our last session, we were running a unique type of combat, both players and myself discovered we had missed things, so the table decided how far we would roll back the combat.