This is a category mistake. Treating bacteria (foreign pathogens of an entirely different species) and treating cancer (which are rogue cells belonging to individuals) are not the same thing.
What you're describing is the normal pharmacological approach to cancer treatment. Because these are the individual's own cells sharing the vast majority of its characteristics with normal, healthy cells, you have to go deep into the handful of mutations that occur that cause unmitigated cell proliferation (leading to cancer). These are targeted for treatment.
Bacteria are a foreign species and have all sorts of foreign biochemistry that can be taken advantage of. The health industry is not doing anyone a disservice by going after the low hanging fruit. Why climb through the 3rd story window when you can waltz through the front door?
Boosting the body's defense mechanisms could carry more risk that just attacking the organism. Boosting chemotaxis (WBC migration) to an area will increase inflammation which has it's own set of potentially dangerous risks. Sensitizing the adaptive immune system's to bacterial antigens runs the risk of autoimmune attack on similar-looking antigens in the host.
This isn't like D&D where you can take one point from "bactericidal" and put it into "immune boost." There are big systems in play and hardly anything can be reduced "one weird trick."
> Look at the molecular machinery of the Polymerase Chain Reaction which makes copies of DNA molecules
Antifolates, topoisomerase inhibitors, imidazoles, rifamycins are classes of antibiotics that target pathogen DNA/RNA synthesis.
> Not to mention the Ribosome which is the molecular machine in your cells which manufactures protein molecules https://en.wikipedia.org/wiki/Ribosome
Aminoglycosides, tetracyclines, oxazolidinones, peptidyl transferase, macrolides, lincosamides, and streptogramins are all classes of antibiotics that target bacterial ribosomal units.
> And there is Reverse Transcription which converts RNA molecules to DNA molecules
Using reverse transcriptase pharmacologically would undoubtedly be dangerous, difficult, unnecessary, and ineffective. You'd basically have to engineer a virus that knows how to use reverse transcriptase that also targets the right pathogen and rewrites a portion of its DNA.