Coaxial or triaxial or even quadraxial speakers are speakers of convenience and ease of installation. They appeal to the masses who just want a drop in replacement that is better than stock. In some I've heard that doesn't always happen. In general, they have very poor crossover components for the above given reasons. That is, in comparison to what they can be(like in a high end component set) when space and cutting corners is not an issue. Having said that, there obviously is a market for these speakers for the fact that each of us places a different amount of importance on sound quality. And some of us are perfectly happy with a set of $49 Pioneers from WallyWorld. There are reasons speakers cost $49 and other, seemingly similar speakers cost 10 times as much, and almost all those reasons have to do with quality in parts and in the manufacturing process.
All this is not to say there aren't some 2 or 3-way speakers that are pretty decent, because there are a few, but they are not "high end".