I read this entire thread and didn't see what I saw as the transition so I will offer this:
- By the mid-to-late 70s rock became ponderous. Longer songs full of exposition and solos that were just indulgent, not necessarily a critical part of the work.
- The rise of new recording techniques (including digital) and electronic versions of instruments (sythesizers, keytars, etc) created new sounds that weren't adopted readily by the old guard rock bands
- MTV was a huge game changer. Their need tor content drove them to pick up bands which saw value in telling visual stories with their music. Video was already a bigger thing in Britain and Europe than it was in the U.S. so a lot of bands from those countries were picked up when otherwise they might have languished, unheard by Americans.
- Bands on MTV challenged the assumptions of many listeners. Much more danceable music than your average AOR band deep cut. Musicians who weren't afraid to incorporate outside influences, like The Selecter and Joe Jackson. Think what you will of the appearance of the musicians in Adam Ant's band or in Culture Club or Flock of Seagulls but they made great danceable music despite their "non-standard" appearance and ambiguous genders. The Bangles and Go-Gos proved women could rock without having to all wear the same dresses and hairstyles.
To me, the music of the 80s was a breath of cold fresh air in an airless landscape stifled by AOR album cuts and disco's 80 Hz bass thump. Certainly there were hits which were not to be taken seriously ("Shiny Shiny" anyone?). But every "decade" had those. 80s music brought back forgotten elements of rock like danceability and predecessor genres like skiffle and rockabilly. I was a serious student of popular music in the 70s but the 80s made me sit up and take notice.