Bacteriophages are neat but we shouldn't pretend like it's totally surprising why they aren't used. For one, they are constantly evolving so it's very difficult to produce a well-defined stable bacteriophage. The version you test in clinical trials is often completely different from the one you'd get treated with a year later.
Hardly off topic when talking about the dearth of new antibiotics.
As for constant evolution - just put known samples on ice? (I wonder if it would be possible to use DNA printing to load them with a tested genome?) Regardless though, they are unlikely to evolve towards uselessness, and they can't attack human cells, so, does it matter if they drifted some?
Bacteriophages are brought up every single time antibiotics are discussed, and always framed as some incredible low-hanging fruit left by the soviets that Americans have stubbornly neglected. I think you really need to keep the discussions more focused than that, especially when the article is about the development and impact of this particular antibiotic.
Otherwise, we end up with the comments for every article touching on city design just rehashing the same arguments regarding car-pedestrian trade-offs ("Did you know that Big Auto had a master plan to kill off the LA street car system!?!?"), and the comments for every article on military jets bemoaning the loss of the A-10 Warthog.
While ycombinator tends to be inhabited by professional and intelligent men and women, they hail from a number of different disciplines and backgrounds. That is to say, Hacker News is not an antibiotics specialist blog/forum, and people would like to converse and learn from others more broadly than you are demanding.
It has nothing to do with training in antibiotics, or anything else biological, as I have none. I have seen the identical arguments rehashed here a dozen times, and they are low quality. (As JulianMorrison's comment, where he does not mention the very first objections in the wikipedia article, and then dismisses them based on laymen intuition when questioned.)
https://en.wikipedia.org/wiki/Phage_therapy#Safety
But more importantly, your comment is off-topic.