The people here are being too hard on the guild master.
Firstly, the bugs are not a threat to the city. They nested back when the mayor's great great grandfather was alive, and nothing happened to the city even now.
MC asked to eliminate the bugs but didn't give an urgent reason for it, so it got denied.
Secondly, the whole reason that high ranking guild set up a base in such a remote city was to look for that dungeon. They didn't arrive at the city to take civilian requests, like small guilds normally do.
Obviously they're gonna focus on the dungeon search rather than accept a high-risk non-urgent high-budget quest.
Lastly, you people got too used to manga where people risk their lives for charity. This guild is an organization, and you can't just upend an organization's purpose to help one friend.
Good luck trying that in our world. It's like a section manager using her company's cafeteria services to host a friend's birthday right when the company is in the middle of hosting a convention.
I'm actually respectful of the guild master for handling the matter as professionally as she can.