Because I have been trying to educate/inform at least three doctors and two nurses at my local clinic on matters related to trans and non binary for about a year with no luck. Their apparent lack of understanding and/or interest in our healthcare is appalling.
This is not something I overtly display for them though, since I'm the nicest person in the known universe - prove me wrong - but having to explain and defend my troubles and legitimacy as a human being that is supposed to be equal to that of cis people does make me bitter.
So even if they happen to know about testosterone blockers, the use cases they know about probably pertain to treatment for hair loss, prostate cancer and other ailments unrelated to gender affirming healthcare.