>At my recent companies, I've even seen senior developers, people with fancy degrees and 200k+ salaries, write code that's horrendously hard to understand and maintain, because it's endlessly duplicated and squashed into a single long function.

Ever wondered that they might be senior and commanding those salaries because they think and program a certain way? Have you ever discussed this with them? Many senior developers tend to shy away from abstractions in my experience, and they do it for a reason.