Why is almost every modern anime 15fps and so choppy with obvious missing frames? Yes they arent using classic drawing techniques but actually cheap cgi but how did we go from this in 1987 to this modern crap?
Here's my theory.
When animation was born, it was about showing it off. It was about showing people how drawings can move like real life. It's fake but it's alive! Look at these funny characters move!
This is why the old 30's stuff looks so smoothly animated, because they were using all 24 frames. There was a different, actual animation cell in every frame. Because it had to look as good and convincing as possible, otherwise what's the point even trying it?
That created some high standards. Being an animator was a hard job but people had passion for it and were motivated to create the best looking animations. This is how animators like Chuck Jones, Richard Williams and Hayao Miyazaki, among others, unleashed some of the best stuff in the animation industry. This is also how early Anime was born and why the 80's 90's ultra detailed animation sequences were a thing. These clips you shared is a bunch of animators going full nerdgasm about their craft: "Look what i can do!" It doesn't add anything to the story (we'll get to that) it's just showing off how great animation can look.
Some animators like Richard Williams even took this way too far, to the point where he could never finish his projects. But he did Roger Rabbit and that one is exactly what i'm talkign about. The pinacle of "showing off". There's even the phrase "bump the lamp" about a scene in this movie which became a catchphrase for when someone goes above and beyond the requirements to show off and 100% describes what i'm talking about: The passion.
Animation used to be mostly about showing off the animation itself is where i'm getting at.
And then, some hacks (like Hanna-Barbera and whoever else followed their steps) decided animation is too expensive and laborious so they tried to dump it down. They decided animation is not about the animation anymore. It's about being able to produce as much of it as possible, despite it's quality. So it's not about showing characters move and making hard to animate visual slapstick, now it's about having a still picture of a bunch of drawn characters talking while only their mouth moves (which is a shame because this studio made some amazing Tom & Jerry shorts before that). So let's cut down the frames, lets cut down the detail, let's reuse as many frames as possible. They found huge success in TV production with children cartoons (because children don't really care) and i blame them for lowering the standards.
Anyway, this line of thinking destroyed the animation industry IMO. Nowadays animation is only about the characters, the story and the dialog, the animation itself is only the delivery mechanism and nothing more. Just look at the modern Looney Tunes stuff VS the classic era. Notice how the modern stuff is about the story and how much dialog there is. While the classic stuff was about the gags and there were episodes where not a single line was ever spoken. The animation itself and the comedy was enough for people to invest their time to them.
So yeah, we care about the story now. So what's even the point of animation, might as well watch real actors. Well, animation got even cheaper in the digital age (skeletal animation, for the love of god!) with tools that automate and simplify a lot of the process and the standards are now so low that you don't even need to be a slightly decent artist to work in the industry. Literally anyone can, the same way anyone can flip burgers. You won't ever see another Chuck Jones any more, or Richard Williams, etc, and when Hayao dies he will be the last of his kind. There's no passion anymore in the industry and people who are passionate end up making some impressive Youtube animations and that's it.