They really aren't. My house is a 1250 sq ft 4 bedroom house. It gets comments from friends and family for being relatively large for a 4 br here, since the norm is 1000 sq ft for a 4 bedroom. Similar style houses in the US seem to be about 2000 sq ft from a property search.
In the US, a 1200 sq ft or smaller home would be a post ww2 "starter home", usually 2 or 3 bedroom. Homes of this size are pretty much not being built anymore, the average size of a new home in the US has been around 2500 sq ft for decades now. The median size of all existing homes in the US sits just north of 2000 sq ft.
Yes, even in a lot of south american countries, for a upper middle class perspective, 1000 sq ft for a four bedroom house is a bit on the small side.