The guild is a democratic body of adventurers, run by adventurers for adventurers. The guild master is one of three powers of the governance of Neverwinter, the other two being the royalty and the churches, he/she is nominated and voted on by the guild members. He/she is a high ranking adventurer, there because he/she deserved to be there.
What you don't understand is the guild is one of the three arms but in reality it is the most powerful organization in Neverwinter, not by class like the nobility or monetary means like the church, or even birthright like the royalty, they are because they are powerful through legitimate means, by powers earned, learned and granted by gods without the authority or rule of a god demanding worship or a leader's lust for power.
Your power grows by your own blood, sweat and tears, your own bravery and cooperation, your own leadership and support of those around you.
If you don't support those values, only then may the proctor reject you and that's entirely up to them.
