Umbrellas work fairly well in steady rain, but they're not too useful on sunny days when you might happen to pass a lawn sprinkler once in a while.

Health care takes place in steady rain. The goal is to reduce exposure below the viral load required for infectivity.

If you walk around with an umbrella on a sunny day, you are bound to get careless.

By the time a member of the public has a rare high-risk interaction, a mask is not going to seal around your nose, or it will be open at the sides, or moisture from your breath will have compromised it, or it will be incompetent due to being long past the very short mandatory replacement time.