In India, practically everyone, and their great-grandmother-in-law, wears flip-flops at least at home. Some wear them to work! And that's a lot of 'some' in this huge country. For one thing, the rubber and plastic ones are pretty indestructible---a big plus for the lower middle classes and less privileged, in our climate and general messy environs. For another, being able to wash it is a big plus, again thanks to said messy environment.
They are called Hawai chappals here, for some reason. (It's odd because Havaiaanas only just turned up a couple of years ago here, and are considered ridiculously expensive by most people.)
I confess my house slippers tend to be flip-flops in summer, and I wear them to beaches and pools too. But they aren't my first choice because of the toe post issue---hard to find comfy ones. However, they do let me grip them, unlike other slip-on shoes.