I've seen a lot of rabbeim (in general at many yeshivas) either wearing nothing, or only a face shield, which is basically useless when used without a mask.
If the maggid shuir, who is usually speaking loudly and projecting, isn't wearing a mask, it's likely to spread if he were contagious as masks primary protects others.
Of course, none of this is to say that any single precaution such as masks is foolproof.
