Earlier quoted context omitted.
Because people would build for that instead of Win32.
That is a valid concern. On the other hand, win32 has a strong developer community with 20+ years of legacy as the primary API of Windows. Now only if Microsoft hadn't try to screw its own developers by trying to push a new framework every 5 years.
Incumbent MFC, Winforms and WPF stuff will live as long as VB6 did (and still does) though.
Edit as HN won't let me reply (submitting too fast). In Europe and JavaFX also has hardware acceleration as does CEF as it uses Chrome's rendering engine.