Yes, you need the game specific runtime formats and for user generated content the toolchain used is relevant. Some of the most popular games with modding support had model and animation import locked behind proprietary solutions that were used when the games were created. Nothing wrong here, but if this toolchain used more open tools, the entry barrier is lowered and import/export would be much easier.

Sure, at some point people created specific plugins for Blender as well, but it creates additional hurdles. And the middleware used is also important. Havok did pose problems for import/export of models in Blender. Of course these are other licensing constraints again that are not only affecting Blender.