A better question might be why shouldn’t they? I’m not being pedantic (at least not intentionally) but if their defining characteristic is that they’re nothing special, just a simple Linux distro that does the basic shit easily enough and looks nice - that has major appeal to people unfamiliar with Linux looking to leave other OS’s behind. The vast majority of people that use an OS really have very little idea how it works or why. They just want some basic level of understanding and control over it.