Apple sold 240M iPhones in 2021 - 15x as many as the 'massive hit' of foldables... I think you're living in a bit of a bubble if you think they're that popular.
Again, not comparable. You're comparing two models against an entire company. It's really Android vs iPhone, and in the Android world those numbers mainly in one model is a massive success.
Given that Samsung sold around 20-25 million S21s, it is absolutely a massive hit.