Because of two reasons:
1. Windows architecture is far superior to Unix architecture which is essentially from 1959 and did not substantially change since then. Windows is far superior technically.
2. Linux has no binary backward compatibility and very limited source compatibility. They regulrly throw away APIs and toolkits making it necessary to rewrite all software. They have thrown away Qt1, Qt2, Qt3, Qt4, GTK1, GTK2, with all software that used them! Windows did so only once, with Win16 (and, yet you still can run Win16 software on 32-bit Windows versions), and attempts doing it second time with all that "Metro". But essentially, Windows API is stable from 1995 till now.
Biting the hand that feeds IT
