1. "Not invented here" (western medical practice largely ignored the USSR, where phage treatments were a big thing: journals didn't get translated, treatments didn't get picked up).
2. Not profitable. They were developed in the Soviet bloc hence not patented but it would have invalidated any patent in the west, so there was no lucrative monopoly to pursue.
After the collapse of the USSR western antibiotics flooded in; the home-grown technique (which was somewhat time-consuming and expensive: matching a phage to an infection requires lab work and specialist facilities) was undermined and fell into disuse.
It could potentially work under Pharmacopeia / Value-based healthcare model, and as a service it's less like a drug and more like a "process"; more like surgery, less like a pill. "Surgery wouldn't work under the pharmaceutical industry either"
The difference we have now vs. 80 years ago Soviet Russia, is that we have tools that speed up lab work and the pipeline of "finding/getting/checking/manufacturing/using" the right phage for the right infection.
It's still going to be mighty difficult, though. And not sure if the economics really would make sense, but still — do the economics of surgery make sense? (I actually don't know the answer to that)
Your assumption is that the medical industry is profitable. This is not universally shared.
I am in the UK; we have socialized healthcare here. Lab work is an overhead, not a profit centre.
(Antibiotics can be prescribed instantly on demand by any doctor. Whereas phage treatment requires a sample of the infective agent to be obtained, cultured, then tested against a library of phages. All of which is time-consuming so renders phage treatments only really useful for severe infections causing hospitalization. At least, that was historically the case: rapid DNA sequencers could in principle turn it into something that can be rolled out to GP practices. But this tech didn't exist even a decade ago.)
It's pretty easy to buy phages in Russia.
It is sold in almost any pharmacy, doctors sometimes recommend it, you can check if bacteria sample is sensitive to phage in almost any medical lab.
I even had an experience of treating infection with phages myself, as antibiotics had interactions with my other drugs. It went pretty well.
But in my case, course of treatment with phages is around 100$, while course of treatment with antibiotics is 5-10$.
which is good, then you can't "preventively" use it on cattle, pigs, chicken etc. like they do with antibiotics, causing resistant strains to develop. I imagine phage therapy would only be an additional "line of defense" against resistant bacteria, similar to the "reserve antibiotics" (which are however more and more widely used, including for animals, despite their "reserve" status).
2. Not profitable. They were developed in the Soviet bloc hence not patented but it would have invalidated any patent in the west, so there was no lucrative monopoly to pursue.
After the collapse of the USSR western antibiotics flooded in; the home-grown technique (which was somewhat time-consuming and expensive: matching a phage to an infection requires lab work and specialist facilities) was undermined and fell into disuse.