Or in software terms, BigCorp sponsors you to develop an open source tool fulltime. If you make the tool more useful for them while making it more complex or worse or ignoring things for others, they might fund you next year as well. If you don't develop things that help them, they might stop and send that money elsewhere and you will need to get a normal job instead and drop your tool work to part-time. Even though they aren't dictating anything, what are you incentivised to do?
The only times this actually happened are C++ and CORBA as far as I remember. Both of them were bureaucratic design by committee efforts from the start, the people doing it weren't users but implementors looking to stop competition, and it all happened before the open source era.