The thing about testosterone being a controlled substance means that acess to it for hrt is restricted. While it makes access a significant issue for many people and an easy and effective way to prevent trans men and mascs from transitioning (as we've seen terfs campaign for and succeed at doing in Britain) it also means that is very easy for health care professionals to be able to take it away from trans men/mascs arbitrarily. This is most aborant in cases where trans men/mascs are forced to detransition to gain access to abortions after being raped. However, the first sign of an issues tangentially related to hormones a gp, without any training in trans people or hormones, can and will stop a person's testosterone. Apart from how stressful it is to know that for the rest of your life you'll be dependent on the goodwill of a random person, this has measurable negative consequences for a trans person subjected too it.

Going off t fucking sucks at the best of time, but being forced off t will most likely result in depression and worsening mental health for a trans man/masc, who are already one of the most likely groups to attempt suicide. It can also put a trans person at risk if they suddenly start being visibly trans again, especially if they're closeted in, say, a work place environment. Trans people, including trans men, are already one of the most targeted groups of harassment and violence and sexual assalt and forcibly reducing or stopping t can out people and risk their safety. And a gp won't see this or care about this, or attempt to treat a trans man/masc first or ask for their opinion or situation.

Ultimately, testosterone is seen as entirely optional and so the first resort when something goes wrong it to take it away, when it should be considered the last resort, and is considered the last resort for cis men. And as long as testosterone continues to be a controlled substance it will remain like this.

(edit for clarification: I am a kiwi, this post was intended as a general critique of accessing t through health care systems - based in my lived experience in NZ and what ive heard from international trans ppl; including but not limited to the USA)