Why is 80s music lacking in bass?

Depends on what you are listening to and the band's decisions. Not quite 80s, but Metallica released an album with nearly all the bass guitar ducked. On the other hand, something like Duran Duran or The Police wrote their music not to thump, but to have the bass guitar actually carry part of the melody. Modern music uses bass quite differently than older music, and what many people think of when they think about "bass" is usually the really rattly sub-bass that only subwoofers can really produce.

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.

There's a whole genre from then called "Miami Bass". See also Detroit/Chicago House. All full of 808 goodness.

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.

Because CDs ushered in an era of crystalline highs that were never captured well before. Vinyl and tape are good at capturing lows, not so good at capturing highs. After decades of muddy sound, they were thrilled to capture the highs. They overreacted and focused almost exclusively on the highs to the detriment of everything else. That's probably what setup the mega-bass trend in the 90s.

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!

Recording media at the time didn't do well with the "big boom," every sample maximized, sound mixing trends that came with CDs. Record needles would jump tracks, tape would print echos on the reel.

They have remixed a lot of 80s music.

I think the question for me is, why does modern music have such heavy bass?

Bass is 30% melodic, 70% percussive. For live music if they are out of sync with the drums you may as well give up. Music today today is often far more percussive in style The bass is a big part of that.

Idk, there’s a ton of heavy metal bands from the 80s and death metal too that are very very heavy on bass.

It’s the genre that matters not just the time period

Maybe because not everyone wants bass assaulting their ears like modern "music".