Epic doesn't want the Wii to fail. They just couldn't care less if it succeeds. They're a PC developer by nature, so it's no surprise they create games for 360 and don't even have the Wii on their radar. As for the iPhone, it's the dominant mobile platform, so of course they'd port their engine to it. And they ported their PC engine to 360 and PS3 because they could do so without having to rebuild it from scratch.
Nintendo HAS created an industry within itself, and that's exactly what they wanted. Hardware that's willfully less powerful than anything else out there, a controller unlike anything else out there, mediocre online with goofy friend codes...Nintendo has done nothing but their own thing this generation. You can't blame third parties, who just want to create games that will sell for as many platforms as they can while re-using assets, for not wanting to bother with Wii. The Wii necessitates its own teams, and that's just not worth it for all but the largest developers.