This is the answer. 4-door benches are about 8in wider at the base because they go forward of the rear wells, whereas the 2-door seat needs to fit right between them.If you have a 2 door, a 4 door bench won't fit due to the bench being narrower because the wheel arches intrude in that space.
@CartmanYou're the second person in about a month I've seen ask about it for pretty much the exact same reason—they want to fold half the bench. Will you always need 3 seats? It might be possible to do something like @Tredsdert did and install a small seat in place of the bench. Unfortunately he has deleted all (most?) evidence of this, but there are a few references to it. If you go that route, I'd recommend bolting it to something more substantial than a horse stall mat. Also, I'm not sure what the rules in Slovakia are, like is a headrest required?
Good times! 