Being a trans boy/kid is NOTHING like a tomboy phase and I'm sick of people pretending like it is

A teenager could say something like "I feel unhappy being female and I feel like I was meant to be a boy" and there will still be people telling them that it's just a tomboy phase. Why?

There are many differences in being a tomboy and being trans. Tomboys/gnc women/crossdressers often embrace being girls and aren't ashamed of being tomboys. Puberty is very awkward, and I'm not denying that. But the awkwardness of it usually fades away in 1-2 years if not even shorter.

Trans men, however, are often ashamed of the fact that they're afab, especially trans teens. And even if they identify as men, they can still dress feminine if they want.

If you called a cis girl who is a tomboy a girl, they would be perfectly fine with it because they feel comfortable as women. They just dress more stereotypically masculine. If someone called me a girl, however, I would definitely not be comfortable.

So why do people act like they're the same?