Comment by OkayPhysicist

People can read textbooks on their own, but how many actually do? Even among the subset of the population that does have the drive to educate themselves, most will end up focusing on the immediately applicable, or at least immediately engaging.

You see this with Physics all the time. Even the people who are sufficiently motivated to try and teach themselves tend to neglect foundational knowledge (especially mathematics, but even stuff like Mechanics and E&M), try to jump into the advanced material (Quantum Quantum Strings Quantum Black Holes Quantum), and then fall into two camps: They either complain about how Physics using too much "jargon", or they read a bunch of "qualitative" pop-sci descriptions of the topic and then think they have an understanding of it.

At least with software, you can get pretty far just learning whatever tool is immediately useful to you, but fully self-taught developers still often end up with random holes in their knowledge.