Was there a specific artistic event or change that led to that?
Yes.
It was called Punk.
It arrived in 76, though at that time was something you saw on TV & read about in the papers rather than were actively involved in. By 77 that had changed.
You couldn't 'slow transition' from rock to punk, the clothes & hair wouldn't let you. I was in the 6th form [age 17] at the time, in the UK. People would go home Friday with one look & return Monday morning with a new one. Bearing in mind we all had a standard uniform so changes still had to fit within that brief, but flares/bags turned into drainpipes & hair went from long to short.
Look at most of the real punk bands from that time & they all actually tend to have 'schoolboy' haircuts, rather than the technicolour spiky of the 'TV punk'.
Those previously hugely successful bands were now universally branded as 'Dinosaurs' & almost overnight lost their market.
Punk itself really only lasted a couple of years. By 79 I was in a band that would far prefer to call itself New Wave... post-punk; often smarter than the original & played by people who could actually play. This hadn't been a barrier to entry for punk [though of course the good ones, Pistols etc had some very good musicians in the studio.]
While this had been going on, another movement had been quietly starting.
By 1980 there were clubs springing up which tended to brand themselves as "Bowie/Roxy". They were playing these artists, including lesser-known material from Heroes etc & bootlegs of live performances, but within a year they were filling the air-time with others, such as Human League, Ultravox & Gary Numan.
In 1980 I'd left my old New Wave band, had joined up with a guy from another post-punk band; we bought ourselves a couple of synths & a tape machine.
Why? Were we following a fashion?
At that point, no. We couldn't be, there wasn't one as yet.
For some reason, England at that time had almost an osmotic effect on musicians. This stuff was just absorbed without even really being aware of where it was coming from.
A&R departments in all the record labels spotted this rising phenomenon & within 6 months we had our first record deal.
It didn't even have a name yet, it would be another 6 months before someone called it New Romantic.
Synths took over the entire sound of fashionable music over the next couple of years, but people started blending in guitars again; a fusion of 'old' & 'new'.
By 83, the shine had worn off the original pioneering sound & this fusion had become the norm.
Enter Trevor Horn, already known [vaguely] from the Buggles, but a rising star in his own right. Frankie Goes to Hollywood's Relax firmly nailed his star to the top of the list & he followed that with a series of more & more finely-honed productions.
Then came Yes: Owner of a Lonely Heart.
In fact the title track is the only one on the album that bears Horn's signature sound, but the path had been set.
No longer branded as dinosaurs, older rock & prog bands were once more free to join the fray.
If they were wielding synths as part of their armoury, they fitted in perfectly with the post-New Romantic sound & were once more free to roam.
It didn't just apply to prog rock, 'heavy' rock went the same direction; usually from the US in the earlier years.
Somebody bought an Oberheim, never touched anything except the presets [these were rock musicians, not synth programmers] & hello Van Halen: Jump.
TL:DR
Punk made them obsolete.
New Romantic gave them a second chance.
Additional note:
I think Pink Floyd got lucky in their timing. The Wall arrived just late enough that people had forgotten they 'weren't allowed' to like them any more.
