The GPL imposes major headaches / restrictions on potential adopters. This reduces uptake, which reduces contributions, thereby reducing sharing of improvements.
And your claim of restricting potential developers is entirely speculation. e.g, see Linux vs any of the BSDs.
There is something contradictory about requiring others to act "more freedom promoting."
Other more "permissive" licenses can be used to constrain anyone though, because the developer sees the license was only for him, and those permissions are not relevant for his end user.
I "care about patents" -- does that mean that I want users to not violated my patents, or that I want to grant my users a license to my patents?