I use it, but I get why some people don't. I remember in the 90's having my eyes on a spirit folio sx and being excited about the routing options on that. Friends of mine that were making 'tunes' and stuff I liked, didn't really get the point, and when they had to have it it was out of necessity to combines sounds sources. For me it was the hub of the whole set up and the thing that set the sound, even though it wasn't a mixer you bought for anything more than a clean sound, but the access to balancing the sound made the sound.
If someone was never exposed to hardware mixers, it may seem such an obscure concept, that having used them we can't fathom.