I know it's not the case because the studies basically are for a wider population set than just transgender people... But even if it weren't, even if it was to create a population of trans mice to use for experiments benefiting trans people; we need it.

People rag on about the possibilities of regret for the transitioned but it is so statistically rare that it really isn't a huge problem... but one of the actual risks of existing as a trans or intersex person is medicine in general doesn't test or teach for your population. Trans people are very often given entirely wrong doses of meds because of assumptions about how they should react to them. Rule of thumb is that the adage that for anyone on horomones "trans women are women, trans men are men" is basically the way to go. This is because if you treat an Assigned male at birth person on feminizing estrogen like you would a phenotyical cis man for purposes of dose chances are that you will give them too much. The drugs will linger in the paitents system just like drugs do for cis women and we already know that is a great way to cause unwanted damages to the paitents' organ function and for desired care outcomes to tank. There are also some meds and health conditions which do have unique presentations in populations with mixed sex characteristics and a more in depth understanding of the nature of sex and the body is how you get cool new things.

There is a largely empty hole in medicine where trans and intersex people are concerned and having an army of "transgender" mice to test against actually would be something of benefit. I know this is a generally unacceptable thing to point out to transphobes however because in a lot of ways they just want being trans to be riskier to force people away from considering being openly trans as a viable option.