Because for police departments, they are a huge benefit and well worth the cost. A lot of crimes have been solved with Flock cameras. Stolen cars, or cars linked to criminal activity have been tracked and located. Missing persons have been found.

None of that justifies the massive invasion of privacy that these cameras represent. You don't have a right to not be individually surveiled in public, but that doesn't mean it's OK for the government to warrantlessly track everyone everywhere they go 24x7, or to do it by proxy with a private company such as Flock. The potential for abuse is just too high, and we've seen many cases of that too.