They used to be called "Dunkin Donuts", I think the name changed to "Dunkin". They are a widely known brand in the United States.

I've never been to their coffee shops but the coffee you can buy of theirs at the grocery store is alright.

Its convenience but also around here, the private coffee shops that aren't commercialized are more expensive.

A bit of both, I'd wager. Same goes for fast food and whatnot.