Most recent study of survivability of vaccinated and unvaccinated. The other major reason is if you are vaccinated you can still test positive but the effects are much lighter. A lady I work with was unvaccinated and will be on a Rx of several meds for the rest of her life due to lung damage.
The most concerning issue that seems to be getting clearer is vaccinated people shed the virus at the same rate as unvaccinated when they are positive This pandemic may only end in a couple generations of immune systems adapting through genetic adaptations. I am diabetic, getting the virus is pretty much a death sentence with my compromised immune system. With the vaccine, the numbers are really good for diabetics.
https://www.wsj.com/articles/covid-19-study-in-england-shows-few-deaths-among-vaccinated-11631549453