They would avoid proprietary forks (not commercial, that's not the same thing) if they actually defended the damn GPL. Instead, they kept weakening it, kept trying to change the API from GPL to LGPL (and I think they actually did it) and encouraged non-free plugins on CRAN.
The license will need to a better job of protecting work
donated to the commons than GPL2 seems to have done.
The license is fine, the problem is that they didn't actually use it correctly!
Well, this is what happens.