If phages are so extremely niche as you suggest, then how come that they seem to be common knowledge among software engineers?

And you're making an inconsistent comparison: it's not about being an expert, not even about having read a wikipedia article on the topic, it's merely about having heard of that thing existing. A Python dev who has never even heard of Rust or can't even guess what HPC might stand for would be strange indeed. And the same goes for medical professionals who haven't even heard about a whole class of treatment options for a serious global disease problem (and, as a corollary, cannot recommend consulting a specialist).