Mac releases requires that the developer A. do a mac build of the project, which actually ends up being 2-3 builds due to the number of different OSX variations that exist, and B. test those builds, which requires _owning_ a mac, and not everyone has one of those. Or, alternatively, building it for mac and pushing it out to a tester who has one and then iterating feedback that way. Regardless, it's time consuming.
Also, many people have limited Internet upload speeds, so pushing multiple 2GB+ files up a 2-10 megabit uplink is time consuming, to say the least.