I see the same thing happening in metal. When I was in highschool, there were a few genres -- mostly 'thrash/speed', 'death', 'black', 'progressive' and maybe a couple more. In college I kind of got away from metal, and in my late 20's got back into it. After getting back into it, I thought "what the hell happened?!!?" There are now so many genres, I don't even know where to start. The hardcore punk of the 80's and 90's was now a legitimate "metal" genre, and every band that had even a hint of hardcore in it got "-core" added to their label. So now you have 'thrashcore' 'deathcore', and my favorite, 'metalcore'. Hardcore was originally supposed to designate a band that was a punk band that incorporated metal aspects into their songs. So it was already a mix of metal and punk, so what the hell is 'metalcore' supposed to be?? A metal band with aspects of punk, I suppose, but I still think the label sucks.

Then you have 'progressive' added to anything that isn't consistently in 4-4 time. Or the even dumber label, 'math metal'. There are even subgenres of prog now, including the dumbest sounding name ever, 'Djent,' which is supposed to be the sound that an extended range guitar makes when palm muting a low string through some shitty digital distortion.

I don't even want to get into the "post-" prefix either. The first time you see a redditor talk about the "post-hardcore progressive deathcore" band they love, you feel like shooting yourself in the face.