I am not advocating for deporting illegal immigrants such as the ones you describe. I have posted about this before, that illegals such as you describe could apply for some sort of legal status that allows them to remain here unless and until they commit a serious crime.

Fair enough, but that's not what the federal law is today. Past administrations have tried to create a de facto system like that, by de-prioritizing the deportation of anyone who's been here a while and hasn't committed any crimes (apart from those related to their immigration status) - but even that was imperfect, and it's mostly been stripped away by the current Administration.

That's why sanctuary policies exist - as a way for local governments to try to create the policy you describe above. If everyone coming into contact with the police (or government agencies in general) gets turned over to ICE, then they all face the risk (or likelihood) of deportation. So local governments set limits on how much they will cooperate with ICE, so that the illegal immigrants that you agree should not be deported won't be. Because the overwhelming majority of illegal immigrants are the sort that you agree should be allowed to stay, sanctuary policies are typically set so that most government folks don't voluntarily enforce the federal immigration laws.

It's a kludge. Sanctuary cities and states don't control federal immigration policy, so they adopt a flawed and imperfect mechanism to try to keep the ones I described from being deported. Since the GOP fiercely rejects your position (that the immigrants I described should be allowed to obtain some sort of legal status), it's unlikely that anything better will get adopted at the federal level. So local governments that adjudge that widespread deportation of the immigrants I describe would be terrible for their communities end up implementing sanctuary policies.