Hmmm ... well, if I was going to hire, say, a chemist to work in a research lab, I need some way to identify if my candidates have the required skills/knowledge/etc. Now one way to quickly ascertain that is to see if they have a chemistry degree (or master's, PhD, whatever is necessary for the particular role). Possibly practical experience could be enough, also - I know people who have worked up through corporate labs without degrees.

However if someone comes and says "trust me, I've read a lot of papers and watched YouTube videos"... sure, they might know what they need, but how am I going to check? The point of a degree isn't necessarily just to legitimise that knowledge, it's also a stamp that says a trusted entity has confirmed you have those skills and knowledge. I'm not saying it's perfect, but there is a purpose to the whole institution.