They may want to sell, move in themselves, or do major renovations that require the place to be empty. Or they are bulldozing to build themselves. Or they don't like you. It can be any reason or no reason at all. They are incredibly difficult to fight.
Thanks, they have given us 120 days (which is the max I believe) I've just never been evicted or vacated before, kinda makes me feel like a bad tenant even though I haven't done anything wrong.