@starkatt It has to do with the way those styles developed, I'd say? Metal started out as an outgrowth of psychedelic and early hard rock back in the late '60s, and was very much a counterculture thing at the time - that tendency just kind of continued on long after within the genre's own associated subculture, where musical style and scene are very closely associated to one another.

EDM is a little different in that regard, in that it's a collection of scenes and styles that started out mostly separate to begin with - across two different continents with a whole bunch of back and forth between them no less, but separate regardless. The early house and techno scenes for instance definitely compared notes with one another, but the music and the cultures between them (one based in Chicago, the other in Detroit) were two different phenomena from their very beginnings, and as much as the genres themselves have evolved and occasionally blended together, that separation never ceased to be a thing.

Rock has neither of these - it's been mainstream since the '50s and overwhelmingly associated with mainstream culture since the '60s and '70s all the way up to the early '00s, and as a result, after the early diversification into soft rock, hard rock, psychedelic rock, etc, most of its styles that ended up having their own identity (metal, punk) ended up becoming scenes of their own altogether, because they were inherently not what rock *meant* to most people at the time. That said of course, mainstream does not mean inflexible, so as overall musical tastes changed, rock music itself did too - which is how grunge for instance didn't end up becoming its own thing altogether like punk and metal did. Music in general had shifted away from the bombastic sounds of the '80s, and grunge followed along with that - hence, it, and "alternative" rock in general represented rock just fine in people's minds over the course of the '90s and the '00s, and so they became what rock -is-.