I quit software development completely 20 years ago after a two decade career precisely because of this, what I called “Wunderkind Syndrome.”
Every place I worked until then featured a primary software product, and that product was the brainchild of one (inevitably) man, and that man could not and would not explain the product. My job was to (inevitably) support, repair and enhance the product.
At one job the Wunderkind (the Rick) only allowed me file-by-file access to source code as I could demonstrate the need to see each file. If he wasn’t around I could not access the new file, but my deadlines didn’t change.
At another job I literally had the Wunderkind leaning over my shoulder when we came to a pair of labeled GOTO statements in his code. He said “I know GOTOs aren’t popular but those two are very important, don’t change them.”
I took this as a challenge and replaced 400+ lines of copypasta code with one function call with two parameters to a three line function. In an afternoon. Which could have gotten me fired (it didn’t but it could have).
This problem didn’t go away, however. Having moved into information security, I found a network administrator who had a hot backup of the data center running… in his apartment. When he was fired (on my recommendation) he retaliated by calling the corporate ISP (who had not yet been notified of his termination) and throttling down the primary internet connection to 56K.