Why won't my builders keep polishing the statue? They do it if I tell them to, but when I leave and come back none of them are doing it? Is it meant to be this way or is it a glitch?

Because there are other things for them to do other than polishing. They choose activities randomly out of what's available. The game does not save what you selected for them to do before you exited the game, so putting them on the statue and then exiting is not going to help them stay on that task. When you open the game the next time, they will probably have chosen to do something else. Even having "building" selected as their preferred skill doesn't mean they'll only do building activities, just that they're more likely to do them.

Yeah I know that, but what I mean is once they stop polishing it they never polish it again. It's not like they leave and then come back. They leave and never come back to it. They just fix the huts all the time. Seriously, they never touch the statue again lol

I don't know, then. Mine do it plenty... in fact, they're always doing it when I want them to do something else.

I don't have problems with polishers, quite opposite since even my devotees polish it alot (and some have mastered building and devotion before 20th birthday).