Quoted from rai:
I think people were buying it because they like the retro nostalgia vibe like BM66 but myself I’ve not really bought anything on theme alone.
I think that's a big part of this -- it was a game selling theme, and it did sell a lot. I think anytime you sell a lot of games initially based on theme there's going to be more people buying the game and then selling it quickly once they play it. Doesn't mean the game is any worse than any other though, necessarily.