Open source patches are all itch-scratchings. For Scala macros, it's a researcher at EPFL, I believe. I don't think you could write a thesis about fixing bugs in the IDE. So this contributor was not available to submit IDE bugfixes; they _were_ available to submit macros.
It's the same for other contributors. Someone building an app on Scala may be available to submit a fix for some scalability issue they are hitting in production; they will not be available to work on macros, or on IDE bugfixes.
Open source projects get the fixes they get. You can't act like the priorities are set by some central product manager.
So I think it's just not correct to argue that "the priorities are wrong, why are they doing this instead of that, etc." - everyone is doing what matters to them. Some people _are_ working on IDE bugfixes, other people are working on macros. People can do what they want.