So where does this stuff come from about 'most oppressed/vulnerable group'?
Some people said it and other people repeated it.
A long time ago they used to justify it with some "stats", but they've stopped doing that because they feel it would be counterproductive to get people to look at them. Enough people are paying attention, and they've got enough people who will just repeat it without thinking. So now it's just a meme.
The things that used to be used to justify it were things like the claimed "life expectancy" of transwomen being 35 or so, combined with a high homicide rate.
Now, most dead transwomen, by absolute numbers, seem to be in the sex trade in South America. Which is very dangerous for either sex. So what you're seeing is figures massively skewed by that, if not outright cherry-picked. Transwomen computer programmers aren't at risk.
And on top of that the "life expectancy" of ~35 is a distortion from those figures - it's actually the average age of transwomen murder victims. And actually, that's pretty much the average age of ANY murder victim. Or indeed the average age of anyone, really. It's the case of the number coming detached from its meaning.
See also ~40% of trans people "committing suicide". No, that's 40% of people in a self-selecting survey said they'd at some point thought about suicide. And it may even have been adults - I'm not sure. Suicide is certainly vanishingly rare among children, so applying that to children is probably a double stretch. I believe GIDS was asked about this, and they were aware of 1 (or 2?) suicides among patients they had treated ever.