The thing to bear in mind is that, for a few years now, it's been permanently at "sale" prices, and is quite frequently end-capped at the likes of HMV, so it gets a lot of eyes on it when other anime titles might not. Purely from the packaging point of view, it looks like something that'd go down easy for someone who only has experience of anime through Ghibli as well, which combined with the price, likely results in a lot of casual purchases purely out of curiosity.
Guilty as charged.
The same is true of The Girl Who Leapt Through Time, to an extent at least, though I'm going to imagine that's a better movie than Origin is. Last I heard, TGwLTTs lifetime sales was somewhere in the 70,000+ region, which is pretty great given the size of the market.
And it most certainly is!
Yeah, well, but then I regretted it.
As did I.