Library authors have explicitely stated that they will not use the library unless its released as a stable version to be part of the Scala Platform, because one of the main points of the library is interoperability (which you can’t get if you need to release a new dependency).
This was mentioned by @ktoso before
If there is an intention for a library to be part of the Scala Platform and interoperability is one of the libraries main goals of the library (as well as the library being a common dependency for other libraries) then its going to be a lot less painful (and more convincing) for library authors to use the library when its part of SP, because they know they won’t need to update the dependency.