They already are. Weight loss clinics will send the Rx to a compounding pharmacy.
I think you are confused about what a compounding pharmacy is -- at least if you refer to how it works in the US.
It's still expensive, but far cheaper than brand name with similar efficacy. Competition from these programs will likely drive costs much lower over the next few years.
Blockbuster drugs still under patent usually don't have alternative avenues of supply that are significantly cheaper than the main avenue. I wonder what law or regulation allows this alternative avenue to persist.
These are first mover prices.
What's the monthly health cost of being obese?
The reason compounding pharmacies are very useful in the US is not because the process of compounding is useful; it's that they have carveouts in regulations that make it hard for the FDA to control them. When there is a drug that is useful and safe, but not approved by the FDA for the purpose you want to use it, you can often get it from a compounding pharmacy.
Semaglutide is a GLP-1 agonist. There are many other GLP-1 agonists, of varying efficacy and side effects, and many of them which a compounding pharmacy can purchase in bulk at very reasonable prices. However, only Semaglutide has been FDA approved for the indication of weight loss, and being the sole approved product means they can milk their patent-granted monopoly for a ridiculous amount of money. Simply because without FDA approval, you cannot get the other similar drugs for the purpose of weight loss. Unless you go to a compounding pharmacy, which, for dumb historical reasons, happen to have loopholes in FDA regulation, so long as they are artisanally producing compounded drugs tailored to a specific individual.