Why do people make major life decisions with almost complete ignorance?
There's no vaccine for the Common Cold because the cold is caused by hundreds and hundreds of different kinds of viruses. If they ever make a vaccine (which they are working on, in fact), they might have to include at least 100 different strains into a single vaccine just to cover the main kinds circulating. And there isn't that much money devoted to cold vaccine research cause it just doesn't kill that many people.
There's no vaccine for AIDS because it attacks the immune system itself and mutates extremely rapidly. Again, lots of people working on a vaccine, but they haven't been able to overcome the fact that it mutates so rapidly that it appears to quickly defeat anything your immune system throws at it.
There's no vaccine for cancer because every form of cancer is different and 99% of cancers aren't even caused by viruses/bacteria. If it's possible to vaccinate for most cancers then you would need technology far past anything we've developed. (p.s. - not to mention that there IS a vaccine for HPV, a virus that can lead to cervical/penis cancer, but anti-vaxxers don't want to take that one either.) What a stupid inclusion.
There are, however, hundreds of different vaccines out there for the many diseases which don't have those particular issues. And now Covid is one of them, cause more money was thrown at a solution than for any other vaccine in history.