Because the agenda pushers have been trying to manipulate us into forgetting biological sex. In the beginning, things were simple and everyone agreed with your statement on the matter. Then everything changed when the nonbinary nation attacked.

First, they wanted to create a distinction between sex and gender. They claimed to acknowledge biological sex and its unchanging nature while merely expanding gender to mean a different thing that could have more meanings and categories.

Now, however, that they have gotten enough supporters of the several gender nonsense, they are backpedalling and trying to merge sex and gender back into one thing. This would mean that sex would take on the new definition assigned to gender and true biological sex would be erased from public memory.

Their goal is to eliminate fact, so first they prepared their fantasy in front of us and are now showing signs of forcing it on us and applying it outside the bounds they said they would follow. This happens quite a bit in politics and was a strategy used by Adolf Hitler. He would say that he only wanted to take over a small area, and the Allies would let him. Several small areas later, Germany had amassed a large area and was now a force that would not be easily toppled. This is what the TQIA++ has been doing, slowly moving the goalpost forward until now they are deep within our territory, and now will not as easily be defeated as if the gay and lesbian community had simply exiled them in the first place