Our immune systems have Memory T-cells, a Complement Protein system, and several other components to both our adaptive and inane immune systems. The sheer complexity of it is due to millions of years of bizarre evolutionary warfare. Just look at this video that simplifies the Complement system: https://www.youtube.com/watch?v=BSypUV6QUNw .. it's still insanely complex even when simplified.
The majority of vaccines we have today are not byproducts of careful genetic manipulation or breeding. They're other viruses that are similar to the one we want to protect against, but less harmful in humans, or they're inactivity through heat or chemical treatment. The first vaccine was based on horse/cowpox 185 years ago by Jenner, and was tested on random people because thousands were going blind or dying and we didn't have the ethical standards on human testing we do today.
They produce antibodies, yes, but there could be hundreds of other interactions there that help different parts of our immune systems build memory. Our immune system is like looking at millions of years of bad software engineering; microservices that were randomly put together by monkeys on typewriters that randomly got things right here and there along the way.
SARS1 and MERS vaccines resulted in some subjects developing Immunopathic responses or Immune Enhancement syndrome. These new vaccines that are being produced seem focused on just generating antibodies using synthetic proteins, which might be missing a bigger and more complex set of interactions that we don't realize is happening with inactivated viruses as vaccines.