static shapes (normally) do not have collision
making the model align to the grid would be a pain
You can only store axis aligned cuboid collision in a blb, and only 10 of them. A static shape can (based on my test) contain 312 convex collision objects and they don't have to be aligned. The beveled sides of the bed for example,
can not be done with blb collision.
A blb can only contain brick grid information (how do we call this, like where you can place bricks on it) for up to 64x64 studs. That's too small for the bedroom, so you'd need a lot of different bricks. A static shape collision layer however can also support bricks, while being a lot larger.
Aligning the model to the grid would also not be a pain at all.