I would actually love for police to harass thieves even if prosecutors, in the end, would refuse to prosecute them. If nothing else, many criminals are dumb; they might do something dumb while interacting with police and either get prosecuted for that, or get put down on the spot.

However, the problem of prioritization by police is exactly that. Police could be doing any number of things; if the outcome of arresting someone is nothing happens, literally any other remaining work, including the kind that could be expanded a lot - e.g. patrolling - becomes higher priority. But ofc Seattle police for example is so under-staffed that they have trouble with 911 calls and sexual assault investigation backlog.