> had learned how to make myself learn

Someone told me ~30y ago, that the purpose of the higher education is: so you learn how to learn. (okay, ought to be). Not the memorizing, or the get-drunk parties :) Now, whether the system-as-is actually even targets that, is a separate question.

So if one achieves that earlier, yeah, no need to waste further years there.

Although as with most institutional artefacts.. , these diplomas - let's call them <tags> - are still used across the institutions, to prove institution-"tax" has been paid.