Infections aren't always easily fixed; In my latest colony, my only good doctor was on her way to treat my incoming caravan who were ambushed by a pack of man-hunting monkeys, when I was raided by some pirates who had molotovs and burned half my base down (Including my medical room). By the time I had fought them off, I only had one person left conscious to treat himself and two others, but between the bullet wounds, bruises, and burns, there wasn't enough medicine or time to treat every single wound before one of my colonists contracted an infection in their remaining leg.

So my level-1 doctor tried to treat the infection without any medicine, but the resulting treatment was pretty shit and the immunity wouldn't develop faster than the infection. By the time the infection was at 80%, the immunity was only at 47%, and at that point I was thinking "This is bullshit. I never liked this system anyway, I'm gonna change it", And since I couldn't find any disease overhaul mods, this was my solution.