They make the assumption that getting the shot(s) would’ve either prevented it or given them a milder case, neither of which could be definitively proven. They’re also gambling on whether or not they get anywhere from mild to fatal side effects from those same shots. If you want to play Russian Roulette with your health based on something that has been politicized (and lied about) beyond all comprehension, that’s up to you.
The milder cases of covid with people who were vaccinated is not unproven. The stats show most people dying of covid today are unvaccinated and the stats prove people who were vaccinated and get covid have the milder symptoms