If I have more space I'd rather have an aditionnal room, a bigger kitchen and a second bathroom than bigger bedrooms.

I agree, especially bathrooms considering how often you use it.

But with 3 bedroom places under 1,000 sq ft, the rooms are too small for even a Queen sized mattress, let alone a King.

The 2 extra bedrooms are for kids, usually. They don't need big mattresses.

Having 3 smaller bedrooms is way better for a family than US style apartments where it's almost impossible to find 3 bedrooms at all.

Is it really even a bedroom if you can't fit a queen sized mattress? That's an incredibly small room.