I've always assumed it is because they can't do the regular coding themselves. If you compare spending months on trying to shake a coding agent into not exploding too much with spending years on learning to code, the effort makes more sense
I'm in the same boat. I'm 20 years into my SWE career, I can write all the things Claude Code writes for me now but it still makes me faster and deliver better quality features (Like accessibility features, transitions, nice to have bells and whistles) I may not had time or even thought of to do otherwise. And all that with documentation and tests.