To build on what wroot has already said,
Yes this is an Open Source community with many Open Source projects. Spark is one of those open projects, meaning we don't have any paid regular full-time developers working on these projects. Everyone is volunteering and doing it on their spare time mostly. A select few may have their own company's pay them to work on a project because it suits their needs, but that still doesn't give us full time "staff".
Regarding Macs... Apple likes to be different. And that's not always a great thing. Apple maintains their own java, which lags behind the regular releases from oracle and openjdk. Most users use Apple's java, and it causes some things to act weird that would work normally on other OS's.
Basically, it means we need a developer who not only owns a Mac themself, but knows enough about java and Macs to "marry" the two. Currently as wroot said, we have nobody working on Spark that is familiar enough with Macs. 