Because Windows PCs are well known to be friendly to developers, with a lovely, powerful Win32 API that's a joy to use, has no horrible warts and... oh. wait.

Thanks to an accident of history (NeXT) combined with Apple killing backwards compatibility with OS9 down, they have a really developer-friendly API compared to Windows. On a purely technical level, Apple is far more developer-friendly than Windows.

They are doing their very best to shit that all away though, when it comes to the legal and backwards-compatibility side of things. That's one reason I doubt I'll ever spend my money on Apple.