It always amazes me how minimal reinforced concrete structures really are. Most of the time you just need a few inches of slab and some columns and you're good to go. Intuitively it feels like there needs to be more material, but there doesn't.
idk much about the trends in engineering. But beams make the formwork more complicated and reduce the ceiling height (which increases costs), and I think nowadays there are greater pressures and expectations of cost effectiveness. Beams let you have bigger column spacing but you can reduce the need for wide spans through design (especially in residential buildings and hotels where there are a lot of walls where columns can go without interfering).
Architecturally in the 80s there was still the trend, continued from the 70s and 60s, of having aggressively expressed tectonics. During that time architects would have been more likely to want to have the different structural elements (slabs, beams, and columns) put together and expressed very clearly. And you can't express beam constructional logic if there are no beams. So back then there was a lot of beam overkill and a lot of beams sticking out of facades and stuff like that.
There's a good example of that here
https://www.flickr.com/photos/iqbalaalam/17051761672/