Re: Why would you ever want to do this?
Straight of the top off my head.
1. Maybe you already have a large java code base that you can reuse.
2. Maybe you consider Java to have better tool support.
3. Maybe your developers know Java and it's not worth the effort reskilling/hiring for one platform.
4. Maybe you want to write multi platform applications.
5. Maybe you don't want to buy each of your developers another development machine (and a very expensive one at that).
BTW, I've been writing obj-c for OSX and iOS for many years now and given the choice I'd prefer java but that is my personal preference. I also have a fairly large database of development time for various kinds of tasks on different platforms/languages/developer experience and java is for most things much quicker to develop, closely followed by .net.