I think it's not strictly legal issues but one of two things. The first is what I've heard being called "a healthy dose of obscurity". With a large enough pool

I think it's not strictly legal issues but one of two things. The first is what I've heard being called "a healthy dose of obscurity". With a large enough pool of users, there is a finite number of behaviors that would trigger a certain ban rule. To avoid having their triggers reverse-engineered, they say as little as possible. The second is is reasons being subject to interpretation. The risk there comes in a variety of flavors from PR risks to lawsuit risks when a developer are banned for X but there's an important nuance to X that the developer ignores by choice or otherwise. I don't mean to defend anyone here, I'm just hoping that someone smarter than me will tackle this somehow.