It is because it is an interesting argument. It is a real-world Asch Conformity Experiment.
A biological male pretending to be something he is not, is still a biological male. I know it. You know it. Gender Studies majors know it. Parents of transgender kids know it, but due to social pressure a sizable number of people will parrot a thing they know isn’t real. The motivations may admittedly be moral or they may be cowardly, but the thing being parroted isn’t true.
What affects the wiliness to go along? How much social pressure is required to parrot the untrue thing? How does it affect the outcome if you can see harm, such as girls getting obliterated or even hurt, in sporting competition against biological males? Is one willing to support the surgical or chemical mutilation of children to prove their faith? It isn’t the 1% of transgender people who are really being argued over, just like they weren’t really trying to find the matching line in the above video. The argument is really over the massive number of people represented by the fourth guy in the white t-shirt and what makes those people tick.