Thanks for the chapter!
MC should've asked about requests can't refuse or responsibilities of those B or higher. Usual trope is that an A or S rank, sometimes B, will agree to have their home base in a certain area, take on requests by royal family regardless of feelings to hunt down any high rank rare monsters, and require permission to leave the country. This is so the kingdom can ensure if a monster like a dragon shows up they have someone always available and know where they are to send them to take care of it. However, they want said A or S rank person to have roots in the kingdom like friends, family, etc. so won't be enticed to some other country resulting in loss of a strong adventurer at best, and at worst someone who strengthens the foreign country or fights for it against the kingdom.