Convenience!
For me this is a prime motivator. I have sufficient demands on my time that added expense of owning a car is worth the 20 minutes it would take to access the closest virtu-car, and the 90 minutes I save every day driving in stead of busing.
I have enough space in my house for cold storage and a freezer. This means I can buy food in bulk and don't have to go to store as often.
Security!
Landlords kick tenants out out now and then. Rents can go up all of a sudden. My family rented for a long time when I was a kid, and we got booted out of several houses when the landlord decided not to renew to lease for one reason or another; wanted to give the house to a relative, wanted a pile more rent, et. cet.
Agency!
For some people home improvement and 'puttering around the house' is a big source of pleasure and recreation. Many people express themselves with the work of their hands, and owning tools and infrastructure to build things and so forth is important too them.
Finally, NRP's planet money has a great blog about the issue of buying vs. renting housing: http://www.npr.org/blogs/money/2010/11/05/131105373/the-frid...
tl;dr: this is about way more than money. It's about personal value choices