>> Hypothetically speaking, because you can get a better support contract with a closed (or semi-closed) source software vendor.

I knew a guy who worked at a medium size company (few thousand people). They tried to drag him back into an old product he worked on years ago to help because.... They still had one customer paying support on it, but someone realized they couldn't find the source code. This guy couldn't help and fortunately the customer hadn't asked for any changes to the software in several years. So no, paying for software doesn't necessarily mean it's supported in any meaningful way.