As a Millenial™, I find myself rarely going to sit-down restaurants because it's more hassle than I'm looking for to have the host find me a table, then wait for the server to get to me and relay an order to them, then have to wait for them again to get the check, etc etc. I'd just like to walk up to the counter, place an order, pay for it and then pick up the food/have it brought to my table all from the start. I also wander around my little nook of LA by myself often, and it just seems unnecessary to go to some traditional restaurant when I'm just looking to grab a bite for myself and then move on with my day.
And when there is an occasion to go to a traditional restaurant, I'm not gonna go to some giant chain restaurant with a bunch of gimmicky entree items like Olive Garden or Applebee's. I'm going to go somewhere unique and at least seemingly authentic because generally if I'm going to that type of restaurant it's a special occasion, and celebrating such an occasion at a Chili's sounds super depressing. That said, I live pretty much in the heart of a city now where you actually have to go out of your way to get to those chains anyway, as they're usually in the suburbs. Back when I lived in a small town (about 15,000 people), your options outside of chain restaurants were pretty slim, so I understand frequenting Outback or whatever if it's basically all you've got.