You're right it's a non issue, but....

The thing that people forget is serving does not always mean combat. Transgender service people can serve in several different positions and parts of the military.

I get that a lot of people think there's a strong distinction there (depending on branch maybe? Do most people know "Every Marine a rifleman"?). But almost any specialization can (and is) deployed, and I've never heard of enemy forces trying to radio or waving a white flag and saying, "Shit, y'all, we didn't realize your convoy was escorting some Paralegal Specialists and the chaplain. There's an IED about 1km north of your position, we'll stand down our ambush so you can go around it."

Plus, for many people the strain of deployment isn't limited to combat situations, but the daily month-to-month grind of stressful living conditions. I know some people like to mock folks who spend/spent most of their deployment sitting on a relatively secure MOB, but even getting parked at Bagram was hard for some people and I'm sympathetic to that (we have lost people to suicide attacks on parts of the base, and flying into Bagram is terrible).

Even the Coast Guard, while ordinarily under DHS and with significantly shorter deployments, had to deal with their fair share of shit (though I admit I've never heard of an unhappy Coastie).

I'm opposed to a blanket ban, but it's not as if there's some safe corner of the military where it's just like civilian life and we can safely shove people with dysphoria and suicidal ideation.

People who are already in either didn't disclose they were dealing with mental health issues or aren't suffering so seriously that medical transitioning is immediately necessary.