The medical profession is aware, they just aren’t scaled up for use in any meaningful sense - essentially to be able to meaningfully fight bacterial infections with phases a hospital or clinic would need to type the bacteria and screen it against potentially hundreds or more phages (even if they are already specific to the bacteria) to find the ones that are going to be most effective. So, there are time constraints, delivery mechanisms and also logistics to overcome.

A challenge for a startup?

> why medical professionals are not even aware that bacteriophages are a thing

Sounds questionable to me that this is even the cause, to be honest. However, assuming this is true, the main reason I could think for why would be the case if this: medicine is an extremely specialised field. Not only do you focus solely on the human body, but not even the body as a whole, but on what can go wrong with it. The only knowledge a medical professional needs about bacteria, viruses and other pathogens is what they require for them to be diagnozed, what kind of illnesses they convey and how they can be gotten rid of. And not even this is accurate, because within the field of medicine there's even further specialisation into even smaller sub-fields.

That there are also viruses which infect bacteria is of no (direct) importance on the medical field. In fact, it'd frankly be a waste of time for them during their study to learn about phages in any detail. The basic degree alone is already very long and full to the point of bursting. It'd be similar to expecting welders to understand the minutea of all states of matter, because TIG welding uses plasma to melt metal.