Speaking from an MMO gaming perspective, I can confidently imagine this is to prevent a market forming around the skill scrolls, along with parties, players and etc drama of a market as powerful as that. Like she says, everyone who wants one must earn it.
From what I understand of the story so far, it seems like Cream Cheese has that level of authority they do because of this ethic of hard work, and likely the devs share that principle with them and had no problem making that clan as powerful as GMs lol