I am always stunned that places like the Olive Garden and Outback opened and are doing well in Manhattan and other huge cities. It's not just the tourists either (though of course a good part of it is).
I am with you, I don't understand the popularity of them, but do know for example in many areas, people are just comfortable pulling into a place they know. They also know the food will be just so so and the prices not the best, but they know what will be on the menu, and they know what to expect. The local place across the street may be ten times better and half the price, but it's not a risk people are willing to take.
Look at a place like Applebees. They have done tie ins with Tyler Florence for his "brick pressed chicken" or whatever it was called, which was a roasted chicken. People ordered it thinking Tyler was in the kitchen cooking it. They have done tie ins with Weight Watchers listing points values on the menu for a few "special items" which were just regular menu items with a salad instead of fries for example. People flocked for the stuff. Does anybody think Italians eat the stuff Olive Garden serves for Sunday dinner? Apparently so.
That, and to a large amount of people, some of those chains are fancy places that don't cost them a weeks savings.
I don't remember the last time we made a choice and stopped in any of the sit down chains, I'm sure it's been years.