Setting up an exhibition can take many days, and the hours can be extreme. There is limited time between when the previous show goes down, and when the next show goes up.
It's crunch time for the artist, and what exactly is involved will depend upon the show. This is the time when the artist's concept for the show meets physical reality, and since things involve the physical world, there are all sorts of things that can go wrong.
At this point the artist is essentially a project manager. They are coordinating with other people to fulfill their own vision. If those other people need a question answered before they can proceed, then those people are going to be blocked until the responds.
It's simply not polite to let people sit on their asses for a half day waiting for a response.
