That’s probably due to all those sites putting their own authentication mechanism in front of the download instead of just letting the webserver handle it.
Built something like that myself a few years ago with PHP. And while it wasn’t super hard it wasn’t trivial either and not supported out of the box by the common libraries.
Yes the problem is solved, but it’s not well supported where it’s needed.
That’s probably due to all those sites putting their own authentication mechanism in front of the download instead of just letting the webserver handle it.
Built something like that myself a few years ago with PHP. And while it wasn’t super hard it wasn’t trivial either and not supported out of the box by the common libraries.