It is not surprising that the CPAN admins are slow to declare code abandoned and then seize it.

It is not surprising that many choose not to contribute once they realize that contributing requires that "admins (slowly) declare code abandoned and then seize it". You nicely summarize the problem. Thank you.

This is confused. [....] If you have the right, you can develop a codebase where, how, and with whom you like, then you can release it on CPAN.

That seems to me to completely miss the point. Creation as the act of a single person is so very common. Maintenance is where collaboration is most useful. The ability to collaborate before submitting to the rules of the CPAN services is certainly not the problem, for multiple reasons. The need to thwart the roadblocks of CPAN services just to be able to collaborate should be seen as a problem, but, yes, we shall work around that problem.