Publishing is what’s called a “vanity” profession as the pay is low for the most part but there is a certain cache to saying you’re in publishing so most people who work at publishers are a dime a dozen. Also, if Rowling wants, she can self publish and will make exponentially more to Hatchett will end up losing millions of dollars in a business that relies on a couple of successes in order to keep the doors open.
There’s a reason the Beatles created their own record label. They could.