Saying they should support ‘every’ platform is really quite naive - supporting platforms costs a lot of money; if Epic don’t believe they can make a sufficient return on support for a given platform, then they won’t support it because it isn’t worth the expense on their behalf. Windows Phone is one of those platforms.
You do however have the source code. If you think it’s worth supporting a given platform and you can make that return, you can take that risk - otherwise your argument is basically ‘I want you to spend the money on my risky venture, because I don’t want to accept that risk’. I can’t recall who, but as an example one company ported an older version of UE to work on the Nintendo DS, as an example.