I've seen this so much, and can empathize with them. When you have a product that took you years to master, the value that you bring to your employer is wrapped up in that product. So it isn't so much that someone is a DBA, they are an Oracle Database software specialist. You've learned all the quirks so that when something goes south, you "have the answer". So naturally you will have a number of reasons why another product isn't as good.
I feel the same way with Unix/Linux. At one point I was told that my organization may be migrating away from Linux, and redeploy everything under Windows. The management layer really couldn't understand that they would lose nearly every Linux admin on staff (that happened to also have deep understanding of their apps and infrastructure). "Why would someone have a problem with switching platforms -- we'll provide you the training" was their answer. Fortunately we were able to come up with a number of technical (and cost related) issues that the project was shot down.
At sufficiently large companies, deep in-house experience with a given DB technology may be roughly equivalent to a startup engineers deep experience on their companies current monolith.
Companies with large and complex db installations often need the complexity for various reasons that are difficult to escape, even if you're working on a green field project.
I feel the same way with Unix/Linux. At one point I was told that my organization may be migrating away from Linux, and redeploy everything under Windows. The management layer really couldn't understand that they would lose nearly every Linux admin on staff (that happened to also have deep understanding of their apps and infrastructure). "Why would someone have a problem with switching platforms -- we'll provide you the training" was their answer. Fortunately we were able to come up with a number of technical (and cost related) issues that the project was shot down.