I interact daily with people who did not have the chance to go past primary school or to go to school at all. And they did have to learn skills through alternate means. I myself had to learn computing and programming with little to no electricity at home, and only a few people that owned computers (which I had to borrow).

I do agree that you can learn with trial and observations, but it's way faster to have someone transmit the knowledge either in person or in books. And once learned, it is learned, unless you don't use that piece of knowledge for a long time and you forget about it. And it's exponential, learning things enable you to learn more things. You don't have to restart from scratch for similar situation. Like you don't have to learn letters again to learn a new Latin languages.

> Not everybody is capable of actual engineering though, as engineers follow processes and measure things

They are capable of it. It's just that most people don't care about that if there is another way to get what they need (including getting other people to do it)