Why is it hard to install preview and experimental packages?

Since 2021 and after, they're not listed in the package manager anymore. I get the reasoning, unity dropped the ball hard when it comes to delivering so the solution is to vanish. Sound.

Trying to install USD, can't be found anywhere. Everything out there tells you to enable preview packages and install from there, except that's not a thing anymore in 2021.

Finally I find a post deep in the forums about USD explaining the ancient craft of installing (USD) preview package.
This only harms users, especially new users. I had to explain to a new user why they can't install the USD package and how to search google for the magic string to install any preview or experimental package.

Worst part is the documentation itself tells you to install it through the package manager by enabling preview packages, it's the one place I'd expect a correct way to be explained.