People are free to work on it if they want. If no more peole work on it, it is likely because Cinnamon is unconvincing, you say you are a user of Cinnamon, what prevent you from helping them ?
Well, one can always push responsibility downstream. But the problem is not that there are not enough desktop environment options. What is lacking right now is a reasonably inclusive distribution policy toward the Fedora desktop which has a clear path into the future and does not lead to further fragmentation of the Linux desktop. If the "Gnome Classic Session" mentioned by Rahul Sundaram is what it might promise to be, that could be something worth focusing effort on. But just calling for effort without a strategy seems a waste.
As for me personally: I have given feedback to Cinnamon. (In fact, I don't think Cinnamon is perfect, but I think they are taking a sensible approach.) My own expertise is not in C/C++ programming, but then I don't think being able/having the time to contribute code should be a necessary condition for taking part in a discussion on features and strategy.
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