Nobody is asking for professional quality standards from hobby projects. At best, they are asking for hobby projects to advertise themselves as such, and not as "this is a library for [x] that you can use in your stuff with the expectations of [maintenance/performance/compatibility/etc.]."
Resume-driven development seems to cause people to oversell their hobby projects as software that is ready to have external users.
> If you want a mature protobuf implementation you should probably buy one
No software is ever developed this way. For some reason, libraries are always free. Approximately nobody will buy paid libraries.