Could be trying to fix/save shovel?

It would definitely be easier to explain why Wyll has shovel though.

Selune is a Chaotic Good Major Deity who would likely view a Quasit as cute, violent, but ultimately harmless and easily controlled.

If one of her followers bound one to their service she probably wouldn't even pay much notice unless they started taking too many/major evil actions.

As for the Cleric they could hold the same view point or if they were Chaotic Neutral they may just view him as useful and expendable.

You can actually have up to two casters who can summon Shovel, even at the same time if you want to! It's not even a big or a glitch. Just have the other caster talk to Shovel and she'll give them the ability to summon. I think it would be a fun and interesting contrast in dynamic to have a cleric be "cursed" with a chaotic quasit. And maybe some day find a common ground and understanding with each other, roleplay wise :)