An even better question would be Why is it not acknowledged that these kinds of flu/cold-like viruses, such as corona viruses, change too rapidly and don't give you immunity against their next version. https://twitter.com/desertskye1/status/1249795257945993221

It is well known those kinds of vaccines are, at best, ineffective. But well-known things are not necessarily heard of easily if a concerted effort is made to keep such knowledge out of circulation https://drcarolyndean.com/2017/11/flu-vaccines-dont-work/

And often they are much worse than ineffective.
Here you can read some quotes dealing among other things with the imaginary, fraudulent nature of those types of vaccines, from the Stefano Montanari article linked at the top of this thread https://twitter.com/Lubalas/status/1246761077720915969