Essentially you're saying 'that's how they made it, so that's how it is'. The point is, that's an arbitrary restriction. We didn't have to have any bedrolls or snowshelters etc. I mean with the same logic they could've restricted sleeping to just beds. If we could sleep anywhere, a bedroll we be a less useful item, and more difficult feats, like summiting Timberwolf Mountain would not have the same difficulty. That takes a lot more skill than just sleeping anywhere. If you don't have a bedroll, you should take into consideration where you are going and how far you are away from the nearest bed. The fact a player can't sleep anywhere is an intended gameplay feature.