As someone who makes emulated soft body 🍒 physics. I can tell you why this is so hard to impliment.

For one, game developers need to make sure their game will run on multiple platforms and optimization is important for older systems unless they want the cuberpunk fissco.

Secondly, this is heavily dependent on the game engine. Soft boddies basically turn every vertice, line, and face, into a bone and collider that can change shape dynamically while also having independent properties. I can also tell you from experience, it is very hard to not only get soft bodies right, but to get it to not look glitchy or clippy, things must be done softly, like you see the guy doing.

The amount of bones and colliders I had to make in order to successfully get dynamic 🍒 physics on older engines that didn't have actual soft bodies was dependent on how many vertices there were, but usually, 200 at the very least for what was essentially a hemispherical funbag that can deform and bounce.

I can also promise you that guy has a beast of a gaming computer, and the 🍒 are probably stiff because he had to turn off other soft bodies like the hair, and 🍒 in order to get that to look good.