Why do people have such large trailers?

I have a 37' TT. We have two kids and a third on the way. For us, we have family and friends that often come stay so we need to be able to sleep a lot of people comfortably. My parents have a 23' and after having mine, theirs seems tiny. It suits them just fine (just the two of them). For us, the 37' camper is awesome. Every family has different needs, hence the reason for various sizes.