neuron

I think a bunch of reasons make chains viable - cheap, (large) portions, standardized foods, familiarity of items on menu and speedy service.

For a family on a tight income, its a way of going out without blowing the bank. For those who are in a hurry, it is fast, easy and relatively cheap.

For many, if you look around you could probably find similar local fare, but most people would never bother to try out something else, for fear it sucks.

As for ethnic foods, PF Changs and Olive Garden are not remotely representative of good Chinese or Italian fare, but people go there.

Finally, I am sure that patrons love the tomacco, err, I mean, extra salt, in the dishes. Seems to make the food more palatable to some.