I worked for a couple companies during my career whose main product was incredibly complex and difficult to understand. Making a minor change in one component could send ripples through the whole product.

One or two 'superstar' engineers who had been with the project for more than a decade were the only ones who understood the bulk of it. They had job security!

I often wondered if they intentionally created it to be that way out of self interest. It made things rough for all the 'normal' engineers who wanted to improve things but got pushback from them and management.