There were no meaning to mass produce and diffuse music in those decades like there are today. I'm not saying 80s and 90s music was perfect (why pick those decades?), i say the more the demand the more the money the more the highs and the lows.

The "quality" you're referring to, i don't know: you're talking about what features of a sound...fidelity, loudness, dynamic?

Anyway, truly the 80s were the years of trash music...but trash as in metal though.