Ask HN: How successful is NimbleBits?

With some recent articles about how there is still money in ios and android apps. There are a lot of successful companies with successful apps. You dont always hear a lot about how successful they are. Example: Nimblebits. They have a number of titles. Tiny Tower, Sky Burger, Nimble Quest, Pocket Planes, etc How successful are they? I have to wonder if they were super successful why have they not been bought?