So I asked my dad, who eats at Olive Garden and Chi Chi's and such about lines. (note that he also goes to smaller places with reservations, so he will eat in and appreciate different kinds of places)
He said - "People won't wait in line unless they think that they are getting something for their time waiting. You can eat for under $10 at Olive Garden, and the food is just fine. No, it's not great, but it's fine." Plus, he said, "it's not like you can just go somewhere around the corner like in Chicago. By the time you get back in the car and drive to another place, which also may have a wait, you might as well just wait where you are. More people are eating out these days, and they don't expect every meal to be terrific".
When I mentioned Maggiano's specifically, which I know a lot of people like, he said "they want a lot of food, so they wait!"
A few things I also thought of is that you don't need a reservation, you can just decide "I have a taste for Italian" and go, and most of these are fun, kid-friendly places.