Because progressives demand change for the sake of change. It's one of their ways of forcing everybody else to grovel before them. Progressives are totalitarian. They want power over everyone and everything, and it's both personal and societal. They want YOU PERSONALLY to grovel and lick their boots. NOBODY escapes.
The progressives know that if nothing is constant and in flux then the citizens will be confused and easily led. It is as simple as that.