It's only been 1.5 years and I'd say for an animated Adult Swim show, that's pretty good. For contrast, The Venture Brothers released 8 episodes in the same span Rick and Morty released 3 seasons. I think Venture Bros is probably the best show on Adult Swim and one of the best adult cartoons still ever made, but their production schedule regularly makes fans think the show is cancelled after the end of every season.
As for why it seems to be blowing up is because it's part crude humor (a la Family Guy) with a heart of gold buried deep within. More people are just catching on as viewship has increased from season to season.
Eh. I'll praise Rick and Morty for its cool sci-fi anthology style setups but I'd feel weird saying it has a "heart of gold". Maybe something's changed in season 3 (I haven't watched it yet) but I've never really felt that from it.