I don't know how FPC team works internally, but it is my understanding that some of supported platforms are developed by specific people who in one way or another do work on such platform, so it wouldn't make any sense for them to work on areas outside of their interest, need or expertise.
...Windows, Linux, Mac, iPhone, Android, maybe Raspberry Pi...
How did you come up with this list? What criteria was used for it? You do realize that there are other platforms than what you mentioned *and* are not deprecated? For one, you did not mention any of embedded platforms, supporting which, in my opinion, is extremely valuable - including both ARM and AVR (Arduino).
Supporting platforms such as OS/2 these days can be considered exotic, but under specific circumstances, I could understand the need for it - for instance, there could be specific piece of hardware and/or software that you need to interact with on an exotic platform, even if it is deprecated. In some cases, it could be extremely expensive to upgrade hardware/software instead of simply developing some kind of interface for it.
Why go through all that trouble to cater to a demographic that literally does not exist? ...[cut]... I just want to understand the reasoning behind it!
One illustration I can come up with: what is more worthwhile, to support a platform, where a thousand "lazy loosers" can write a "hello world" app to get rid of their class homework and never get to use these development tools again, or supporting a platform, where a couple, maybe two or three, scientific groups work on fine-tuning/upgrading satellite telemetry system? This is just an example.
My point is, FPC's quantitative demographic may or may not represent the actual "worthiness" of one specific platform. In fact, I think, it is a combination of quantitative + qualitative factors that may determine importance of some platforms, which does require a significant research into that topic before it can be discussed like that.