Another factor would be that many of the local restaurants aren't all that much better. Most of the local mom and pop restaurants with similar menus to the big chains are getting their overly processed ingredients food off of the same SYSCO truck as the chains. Obviously this does not apply to fine dining / high end / ethnic places.
The biggest of the chains (Chilis/TGIF/Applebees/Outback) are basically neighborhood sports bars of various stripes. Go to your local mom and pop sports bar, and see how much better or even different the food is. Mostly just the same with some slight regional variations. The burgers at my local pubs are mostly the same as the chains, but with a few local menu items (in my case in South Florida, grouper, conch fritters, key lime pie etc)
If the food is largely similar and the chains offer a better value proposition, then why not eat at the chains? Especially for people with kids etc?
The only time I eat at chains is if I am on the road. I will admit that I have a little soft spot for Outback...