I don't think it's strictly about competence and more about specialism. In my personal experience, which you can take with a large grain of salt, what happens is that the engineering manager with a certain type of career history tends to look down on any type of operations work and anyone who does it. I have heard things that come off sounding like this: "We hire world class computer scientists from prestigious Ivy League schools and FAANG experience, so why do I need to hire some one-trick-pony DB guy, when my engineers could build their own databases from scratch?"