The reason they give is that they don’t want people to be able to hide their identities at protests etc. I think there’s also a backlash against people wearing masks in general because people really don’t like being told that “going back to normal” actually means the mass disabling of the general populace, and the extermination of a smaller group of people with auto-immune diseases etc.

EDIT: Oh and in this specific case it’s also because Karen Bass (the mayor in question) supports the genocide of palestinians.