80s music was intended to be played on a boombox radio with no sub-woofers and still represent all the sounds the band recorded. In the end, it's just one of the ways music has changed over the years.
One of the standouts to me is what you mentioned -- in older music, the bass often does heavy melodic lifting and in newer music, it tends to be mostly just carrying a beat.
Not saying one is "better" than the other -- that's a matter of taste. It's just interesting to note the change.
It's also interesting that if you ignore music after the '80s and just compare '80s to the decades before that, you could accurately say something very similar.
It also depends a lot on what musical genre we're talking about. Not all '80s music was new wave and the like.
Compared to modern music where the instrument isn't limited by the sounds it can physically make (due to digital production) as well as the things they make each instrument do, as you said much of modern music is carried by a beat rather than a melody, so a vocalist might be the only discernible melody. Back to a pipe organ, it would be really difficult to play a modern song on the pipe organ as a result because the structure is so different that it's hard to really compare. However, the pipe organ was a marvel in that it allowed a player to basically BE the entire orchestra if needed.
In the Deep South, at least, go to Sonic drive-in any night of the week and there'd be low-rider pick-up trucks whose beds were filled with 20 inch subs.
Also, any number of cars with the back seats taken out to make room for stupid loud window-shaking bass.
As an aside - going back to the '60's and the evolution of bass - one of the reasons The Beatles stood out when they started was that their lows popped on transistor radios because Paul recorded his amp using a loudspeaker instead of a normal mic.
Along with that, they went crazy with hall effect reverb on a lot of recordings. Everything sounds like it's being performed in a big, echoey concert hall. I'm really glad that fad faded!
They have remixed a lot of 80s music.
I think the non-bass-heavy nature of much of '80s music is more about fashion than anything else.
Subwoofers became increasingly popular through the '90s along with the rise of hip-hop music pushing ever-harder bass, synthesizer technology developed along with the increasing power of computers, and by the 2000s music producers had a new corner of the sonic palette to play with. New genres followed suit.
In the '80's most audio equipment had not been capable of reproducing material which would feature bass as the main element up until that time.
So apparently very few had developed the taste that would have driven them to produce recordings where the singing and melody were less prominent for that reason.
But you can turn up many old recordings on a modern subwoofer-enhanced system and rattle the walls quite effectively, the rest of the instruments will be as equally strident as the bass though, like the producer intended and more like the live concert than the old audio gear would do.
It’s the genre that matters not just the time period