Because it was a cheap win for people who didn't put in a lot of thought, aka the normies on the fence. That was it, the moment you thought about it even a little it fell apart. It was designed to get that foot in the door, wherein you are already nodding to an easy sell while the are already giving you a larger one.

Leftism is like Islam. Its allowed to do anything possible to manipulate you to its side, no principles or logic needed.