Scala 2.10 represents a huge maintenance burden.
The compiler is very sensitive, especially when working with macros, easily crashing with unintelligible error messages that can take hours, or even days to debug, because really, at some point you start editing random source files in the hope that the crash would go away.
And generating ScalaDoc for 2.10, 2.11 and 2.12 is basically mission impossible.
The Scala ecosystem has a big problem in not doing a good job of maintaining backwards compatibility. But given the tools we have, it isn’t reasonable to expect libraries to maintain support for 3 or 4 major Scala versions, along with Scala.js and possibly Scala Native in the mix.