Because it is not the same level of risk. This can be trivially seen by comparing the percentage of health care workers that ended up with severe cases of COVID (or that died) compared to the regular population. Especially in the beginning of the pandemic when it wasn't really clear what we were dealing with and how it was spreading a lot of health care workers got very high doses and ended up in serious trouble. This isn't unusual for such situations, but it is unusual for it to happen at this scale.