But the easiest one I can explain is that this trend was clearly temporary as you and your mother acknowledge. Whereas the history of transgender people in humanity goes back to ancient history and carries through societal trends and gender role evolutions.
The more biting thing I can say is just because "<Something> is a trend", doesn't mean that "<Something else> is a trend too."
It always confuses me how on a site for techies, where people constantly reason about with virtual concepts and abstractions, the idea that physical biology genes and hormones might be typically but not EXCLUSIVELY coupled with mental sentience is so difficult to imagine.