I think that's a side-effect of other primary reasons. People buy a fuel-efficient car as the primary car because they want to keep expenses down. But that little car simply can't do everything.
Right now, my second vehicle is a minivan, so that I can take 6-8 people along for a ride occasionally. When you have kids, they tend to have friends, and it's nice to be able to offer to take all the kids yourself so that your neighbors don't have to drive their kids separately. Everybody has a minivan, and we take turns offering to drive them all. Saves both fuel and everybody's time when people take turns carpooling this way. When the in-laws come to visit, we can all travel in a single vehicle to go out to eat together. It's actually more efficient when that somewhat gas-guzzling minivan prevents the use of a second vehicle.
A lot of households (outside of cities) have a truck as a second vehicle. I used to, and I really miss the ability to go pick up random crap (yes, including fertilizer), throwing it in the back, and not worrying about getting the interior of the vehicle all dirty. That was more important when I was younger, pre-kids, and saving money by buying furniture and appliances from local classifieds (the print version of craigslist, for you young people), garage sales, etc.
2012 Black SV, 8 bars, 98,000 miles