Restaurants, almost uniformly, serve unhealthy food. There are exceptions to this, but they don't seem to be all that popular. When I go out to eat with friends I am often stuck eating something heavier and less healthy than I would like.
Is there some good reason for this?
I'm sure there are exceptions to this rule but restaurants typically have to cater to the lowest common denominator.
Even those restaurants who want to appeal to a 'healthy eating' audience find that their less healthy items sell better; considering the difficulty of succeeding or even surviving in the restaurant business, they start to emphasize those items and eventually become a source of relatively unhealthy meals. It's the same phenomenon that caused all of the niche cable networks to fill their schedules with general-interest reality shows unrelated to their original programming over the last couple of decades.
tl;dr: Restaurants sell unhealthy food because people want to buy unhealthy food.
Thighs are less time and temperature sensitive. They're a bit more hardy if you're new to cooking. Chicken breast is easy to overcook because less fat makes it less forgiving.