Why/Why not? Because it's all part of the vaunted "undermonetized D&D lifestyle" that Hasbro is pushing.
I said it needed to be a "loud" boycott: prompted by streamers and bloggers, picked up by gizmodo or something, repeated all over social media, etc. Obviously, simply not showing wouldn't do anything unless it's been telegraphed why they're not showing. The aim would be the threaten the box-office take on a potentially good D&D movie, specifically by people who love D&D. Presumably it would depend on the relative amounts of money at stake and whatever publicity came of it.
It might mean something. Or it might not.
But there's one way to find out.