Many people choose their car based on their peak requirements, rather than their average requirements.

I've seen people commute in a minivan every day because the space was useful taking their kids' stuff back and forth to college a handful of times a year. I've seen people buy SUVs because they tow a boat or a horse box once every six months. I've seen people buying larger cars so they can transport five adults in greater comfort - even though they only need to do that a handful of times a year.

Now, it's possible that these people would be better served by one car for their everyday needs, hiring different cars for these occasional needs - but most car buyers aren't used to behaving that way at the moment.