The usual narrative around this skill is that it was banned because it was too dangerous, but that doesn't ring true to me -- many release moves performed both by women on the uneven bars and men on the high bar have similar motions whose risk is surely equal to or greater than a Korbut flip.
Compare this with a Mo Salto, one of the hardest (legal!) release moves in the women's code of points: https://youtu.be/eIwTquLwGpA?t=26
On the men's side, the Korbut flip is a pretty similar motion to a Kovacs (https://www.youtube.com/shorts/6yRJaivL1TE) which is a staple of high-level men's gymnastics; in fact the basic Kovacs is "so easy" that you rarely see the vanilla version performed by top athletes! It's more common to do them with a full twist (Coleman/Cassina, e.g. https://youtu.be/8IeBXhijY0M?t=40) or in combination with other release moves (e.g. Zonderland at the 2012 Olympics https://youtu.be/I0TM2sOnvyI?t=1160). Hidetaka Miyachi is one of the few people to ever have competed a double-twisting Kovacs (both tucked and straight! https://youtu.be/RgW36EKyKyg?t=23), and there are a few videos online of people practicing a "double Kovacs" with an extra flip (e.g. https://www.youtube.com/shorts/zI8VEll7wKI) but nobody has ever done one in competition.
While it's perceived danger might have been a factor in the initial ban of the Korbut flip, in light of these modern release moves it's hard to see how that is still a good reason. Instead, I think the reason it remains banned is more aesthetic; bars are supposed to be a swinging event, and we don't want to allow skills that have athletes standing on the bar instead of swinging around it.
On the other hand, banning the Thomas salto (https://www.youtube.com/watch?v=vkQRWCsKyj0) and other similar roll-out moves on floor is very clearly motivated by safety -- these are indeed very dangerous, and athletes have been seriously injured by them (most famously Elena Mukhina who became a quadriplegic as a result of this skill).
Pretty much everything you'll read online says that it was because of the high risk of injury, but in my opinion that's only a small part of the story.
Not denying that risk was part of it, but it was the first move where a gymnast stood on the bar. I think a lot of gymnastics folks felt that it disrupted the overall flow of the routine, and it basically just wasn't what uneven bar routines were supposed to be about.
Things like this happen from time-to-time in gymnastics: someone finds something that is a bit "outside the lines", and then it gets banned. E.g. several years ago a gymnast did a floor routine wearing "cat-like" makeup (Maybe her music was from Cats? Can't remember) and then subsequently the FIG banned "theatrical makeup" in routines.
For example, here's a Korbut flip: it's a back flip from the feet to catch the bar: https://youtu.be/NZYPcdj_wn4?t=15
Compare this with a Mo Salto, one of the hardest (legal!) release moves in the women's code of points: https://youtu.be/eIwTquLwGpA?t=26
On the men's side, the Korbut flip is a pretty similar motion to a Kovacs (https://www.youtube.com/shorts/6yRJaivL1TE) which is a staple of high-level men's gymnastics; in fact the basic Kovacs is "so easy" that you rarely see the vanilla version performed by top athletes! It's more common to do them with a full twist (Coleman/Cassina, e.g. https://youtu.be/8IeBXhijY0M?t=40) or in combination with other release moves (e.g. Zonderland at the 2012 Olympics https://youtu.be/I0TM2sOnvyI?t=1160). Hidetaka Miyachi is one of the few people to ever have competed a double-twisting Kovacs (both tucked and straight! https://youtu.be/RgW36EKyKyg?t=23), and there are a few videos online of people practicing a "double Kovacs" with an extra flip (e.g. https://www.youtube.com/shorts/zI8VEll7wKI) but nobody has ever done one in competition.
While it's perceived danger might have been a factor in the initial ban of the Korbut flip, in light of these modern release moves it's hard to see how that is still a good reason. Instead, I think the reason it remains banned is more aesthetic; bars are supposed to be a swinging event, and we don't want to allow skills that have athletes standing on the bar instead of swinging around it.
On the other hand, banning the Thomas salto (https://www.youtube.com/watch?v=vkQRWCsKyj0) and other similar roll-out moves on floor is very clearly motivated by safety -- these are indeed very dangerous, and athletes have been seriously injured by them (most famously Elena Mukhina who became a quadriplegic as a result of this skill).