>How does someone make videos for a living for 15 years and never get any better at it?
This user has it right: Basically, if you keep making the same mistakes over and over again with no one to point them out to you and help you fix them, you get trapped in a pattern and it only becomes harder and harder to extract yourself from it the longer you do it. It's why teachers and mentors exist, as much as the "self taught" crowd insist upon not needing them. But usually, even the self-taught artists can either see for themselves when something can be improved and diagnose how to improve it, or their audience will give them the feedback they need to identify their shortcomings and figure out how to overcome them.
But if you have a huge EGO, that makes improving your craft even harder. Who is a teacher to tell you how to get better? Who is your audience to tell you where your mistakes are? What do THEY know? After all, YOU'RE the artist; you know what you're doing!
And so Doug, having no proper training of any kind and being much too ego-driven to ever self reflect or accept criticism/pointers, has been making the same shit for nearly 20 years and will never, EVER get any better.