Question: why does natural immunity create the same pressure on virii to mutate into forms that can get around the antibodies? Answer: it does. However there is also pressure on the virus to mutate so as to not kill the host and in principle this is why they fade into the background over time. Yes, they can still spread (see: common cold) but they are a nuisance, not a potential death sentence for otherwise healthy people.
So then the question is why would vaccination make the virus more contagious AND more deadly? That makes no sense from an evolutionary perspective.
That's the million$ question.
Maybe it's because the Chinese hit the jackpot in their 'gain-of-function' quest.
Because they are not real vaccines. They are gene therapy. Totally different.
My understanding is that this effect occurs because the current vaccines are non-sterilizing, i.e. they don’t kill off the virus and don’t prevent its further transmission, they merely protect (temporarily) from some of the symptoms. This is similar to how overuse of antibiotics, and failing to take the full course of antibiotics when prescribed, puts pressure on the bacteria to mutate without killing them off, leading to antibiotic-resistant “superbugs.”
Add to that the fact that we are hell-bent on trying to vaccinate virtually every person on Earth. Widespread vaccination with non-sterilizing “vaccines” creates the ultimate playground for the virus to mutate. If only a small percentage of people were “vaccinated”, the much more effective natural immunity of the unvaccinated would keep the virus in check. Essentially, when every person the virus encounters has exactly the same narrowly-focused antibodies (from the “vaccine”), all it takes is for the virus to hit on one key mutation and it can then evade both the “vaccine”-induced antibodies and the “vaccine”-suppressed natural antibodies in the vaxxed.
There are studies on natural immunity showing it is effective against variants, the shot, not so much.