Why are GnRH agonists so expensive?

tl;dr: Scroll down to the last 1-2 paragraphs if you're only interested in the question in the title.

I've been doing a little research on GnRH agonists for suppressing androgen production and they seem to be superior to the mainstream anti-androgens (spironolactone and cyproterone) in almost every single way. Here are the advantages I have found so far:

• Spiro and cypro can cause carcinogenicity (cancer) and hepatotoxicity (liver damage), respectively. GnRH agonists in contrast are not known to be toxic in any way (when taken with an exogenous sex hormone like estrogen of course; without one, problems with bone mineral density and such can occur; these risks apply to anti-androgens as well of course however) and hence have a better safety profile.

• Spiro and cypro are rather non-selective, affecting the androgen, estrogen, progestogen, mineralcorticoid, and/or glucocorticoid systems in one way or another (depending on the compound in question), and thus can produce many unwanted side effects. GnRH agonists on the other hand are highly selective for the GnRH receptor and have a much improved tolerability profile.

• Due to their relatively short half-lives, spiro and cypro need to be taken every single day. In fact, it's generally recommended that the former actually be taken twice a day. Contrarily, GnRH agonists have very, very long durations of action (when taken via injection) and only need to be administered once per every anywhere from 1-6 months. As a result, they are more convenient to take and maintain a greater consistency in the blood.

• While spiro and cypro can generally result in a relatively satisfying reduction in androgen activity when combined with sufficient doses of an estrogen, GnRH agonists can reduce testosterone levels to castrate levels without estrogen (and hence, the estrogen dose for MTFs could be lowered by as much as half in theory), are more effective at doing so than anti-androgens, and require lower doses to do so as well. They can in effect completely eliminate any significant endogenous sex hormone activity in the body.

• GnRH agonists can work for FTMs as anti-estrogens as well as for MTFs as anti-androgens. However, I'm not sure that they're needed as I believe testosterone alone is generally effective enough as an anti-estrogen for FTMs. In any case, for trans men who want to lower their testosterone doses (after oophorectomy (removal of the ovaries) testosterone dose can be about halved; since GnRH agonists can reduce estrogen concentrations to castrate levels, in theory they could allow for a similar dose decrease) and/or for those who have particularly resiliently high estrogen levels, GnRH agonists can potentially fill the role of an anti-estrogen that, as far as I know, no other kind of drug can.

And here are the disadvantages:

• It can take anywhere from 14-28 days for GnRH agonists to reduce testosterone concentrations to castrate levels. This is because they need to desensitize the GnRH receptor by activating it before any reduction in activity occurs. This also results in a brief, initial surge in testosterone, another potentially undesirable effect. Classical anti-androgens work instantly in contrast and are thus superior in respect to speed of onset of action. However, GnRH agonists can (and often are) combined with anti-androgens at first until they start working fully, which nullifies the potential speed advantage of anti-androgens alone.

• GnRH agonists are extremely expensive in comparison to classical anti-androgens for some reason (more on this below). Furthermore, as far as I know, insurance doesn't usually cover them (as doctors can't really bill them as treatments for government-approved indications, which many of them can and are willing to do for conventional anti-androgens (e.g., spiro as a diuretic)).

Correct me if I'm wrong on any of this.

In summary, from a pharmacological standpoint, GnRH agonists seem to be far superior to classical anti-androgens in virtually every respect, with the sole exception of onset of action (which can actually be negated if anti-androgens are combined temporarily at the beginning of treatment, as mentioned above). Unfortunately however, due to their very high apparent costs they're almost never used despite being the better choice.

So my question is why exactly is it that GnRH agonists are so expensive? Wikipedia says that they've been on the market since at least the 1980s. Hence, I'm sure that there's at least one that's off-patent and as a result should be available as a cheap generic. Yet this doesn't seem to be the case. Anybody know why this is?