New
#31
Sometimes, you have to start over. And it takes some time. Windows had reached the point where it needed to be rewritten, but rather than do this all at once, it's happening in much smaller steps.
Sometimes, when they introduce a new feature in the "new" part of the OS, they have to remove it from the "old" part of the OS, even though the new feature may not be as mature as the old one was. New versions of Windows will come much more frequently though, every 3 or 4 months, so you don't have to wait 2 years for the next OS.