I think none of those assumptions apply in this case, or even in general. If there were no money in it, then the products would not have been actively maintained. VB6 was ranked 20th in TIOBE last year, so it is not just used in my company, either. In fact, if it were so unused, Microsoft would have dropped support for it already, but they currently support it until Windows 10 EOL, and possibly will on Windows 11 as well. I have not looked at the codebase behind the VB6 products in question, but there is no reason for me to assume that it looks any different to any other long-established codebase, or that the developers who maintain it are paid less. I would assume they are paid more because they are harder to replace, which in turn makes their work more rewarding.

I have worked on products with old tech stacks as well, e.g. a C++98 codebase for the core product of a multi-billion-dollar company, with no plans to migrate. New features were being frequently added, and the company's own standard library replacement that bridged the gap was itself actively developed.