Why wouldn't a linesman, electrician or carpenter be able to self educate? We live in the day and age of the internet, the largest store of human knowledge ever to exist is a few clicks and an inquisitive mind away.
I understand that college exposes you to things you might not have otherwise been exposed to, and provides teachers and mentors to facilitate the learning of that material. But if you attend college with the end goal of getting a degree to cash in for a paycheck like so many college age people do and you're not motivated to actually learn the material you're exposed to in any meaningful way and that information isn't retained then what's the point? Certainly that's not all college kids but I'd argue the vast majority are only there because they believe it to be a ticket to the middle class.
I'm a self-taught software engineer who never finished college, so the trade school stigma hits home. I certainly strive to be as educated and productive as possible in my life and career - and so far that path hasn't held me back at all. I'm employed, highly paid and fairly happy, I just chose not to receive that education in the confines of the classroom