The "why" aspect of it comes down to likely overregulation but really some of these small changes can have some pretty large impact on the whole processes, so the "how" also comes into play for a complete answer.

The answer is two-fold. There has been a “shortage” of HCG since a 2020 ruling by the FDA restricting compounding pharmacies from dispensing HCG, thereby further decreasing supply (though a few compounding pharmacies did get waivers from the FDA).

The short of the second part of the story is that certain preparations of HCG are essentially copies of the commercially available products that Big Pharma companies are allowed to make through FDA approved patents. Big Pharma and the regulatory bodies (FDA/DEA) do not allow nearly similar copies of commercial products to be reproduced. Compounded formulations need to be made different enough to be distinguishable from the commercially available products. Certain states are more strict on their compounding regulations than other states. Once a compounding pharmacy establishes their formularies and the state regulations are changed, it can be difficult for sterile IV compounding pharmacies to quickly change their preparations to adapt to meet the new regulations. Moreover, many of the wholesalers that previously carried the purified raw material no longer supply this to the smaller compounding pharmacies after regulations got too strict or too expensive to keep up with. In some other cases, pharmacies may have lost the ability to send biologics over state lines due to the strict restrictions.

In a sense, the "why" also comes from the how - Since if it is more expensive to produce & there is higher risk with doing it, the cost to the end user has to increase proportionally. The end user hasn't liked the increased price, so demand dropped. With lower demand at the available price points, new pharmacies & even some established pharmacies don't see a reason/profit in continuing production or starting it. So even if not completely regulated, the parts that are impact the supply/demand enough to endanger it's viability as a sold product.