A lot of it isn't "need" for more space; rather, it's that all that is available. I've been living in the same 3.3k sq-ft house for 10 years. There's simply nothing smaller in my area. OK, one retired farmer down the road has a house that's about 1200 sq ft, but that's by far the smallest house.

It's a pattern I found recurring as we were looking at houses: unless you wanted a 100 year-old house (which could be a good or bad idea), there was simply nothing under 3,000 sq ft on the lot sizes we were looking at.