I had my eyes opened about this when I was reading about the early days of American punk. CBGB's, the legendary CBGB's, was actually EXACTLY the kind of ****hole that you describe as to blame for killing live music - but it was ground zero for American punk, and later New Wave (Blondie and the Talking Heads came out of its scene). The other thing that really impressed me was how FEW venues those bands had to play in - CBGB's, Max's, and maybe two or three other places - in NEW YORK CITY.
Excellent point. The venues described by the OP have always been around and probably always will be, as long as enough people want some ****hole to get drunk in. If this is bad for the grassroots music scene, I don't think it's the venues' fault. There's a lot more competition for live music these days than there was in the 60s and 70s: TV, video games, internet, etc. There's no use complaining, that's just the way it is.
Meanwhile, my college-age son tells me he attends house parties where kids bring instruments and jam, and young bands will play--it's a thing. So maybe there's hope yet.