Fighting viruses confers immunity to viruses, but bacteria are vastly more complex organisms than viruses. Generally, your immune system can’t “learn” to identify a bacterium the way it can a virus. This is why there are vaccines for many viruses, but very few bacteria, and the ones for bacteria tend to wear off after a comparatively short time, like, a few years, while the shortest lasting viral vaccines last about 10 years (flue vaccines last decades to the strain they confer immunity against, but there is a new strain every year).
Anyway, this is why you get viral infections once (some individuals are rare exceptions), but you can get things like strep again and again. After you have strep, you are immune to reinfection for a few weeks, or maybe a couple of months, but that’s it.
Also, generally speaking, bacteria are lethal when they release toxins-- the toxins are their waste products. A few are dangerous because they cause high fevers or compromise breathing (one reason some are especially dangerous in infants, who have tiny airways, and can’t sit up), but mainly it is the toxins. They overload your organs, and cause them to fail. E. coli bacteria kills by killing your liver and kidneys with its toxins. Strep toxins can cause neurological failure, which is how it causes blindness, and it can affect the autonomic nervous system. The rash that marks scarlet fever is an allergic reaction to the toxins.
This is why you want to get antibiotics early on, before there is a build-up of toxins. You have a few days, which is why there’s plenty of time to make sure it’s not a cold, but you don’t have weeks. Also, people with liver or kidney problems may not have days-- they may not be able to wait and find out if something is viral or bacterial-- they need an antibiotic ASAP, just in case it’s bacterial.
Remember, the people you know taking antibiotics for a viral infection had a doctor prescribe them. Like I said, there are a few doctors who may give in to a whiny patient, and some patients who lie about the duration of the symptoms, but on the whole, if someone with a viral infection is taking antibiotics, there’s a reason. Maybe they don’t want to tell you they take post-transplant immuno-suppressants, or have or COPD, and are at high risk for a secondary infection, or a secondary infection is very dangerous for them, but there is probably a reason, and it isn’t the placebo response. If it were the placebo response, the doctor could prescribe prescription-only antihistamines, or something.