Your analogy about calling the police seems spurious to me. An individual's relationship to local law enforcement is totally different than a major city government's relationship to the federal government. However, the situation is fairly similar to municipal decriminalization of marijuana. Philadelphia police don't hand smokers over to the DEA despite federal laws being broken. In theory, the DEA could send agents to enforce federal law and effectively overrule the decriminalization, but they don't have spare manpower and resources. Admittedly, the DEA doesn't actually want a bunch of minor pot offenders, and the DHS does want illegal immigrants. Also, San Francisco broke an existing precedent of law enforcement cooperation, whereas Philadelphia broke an existing precedent of legal cooperation/alignment. Since they can't generally afford to enforce their law in municipalities that don't abide, the federal government turns to funding to exert some level of control.

It's certainly not laziness that motivates the uncooperative policies. It's simply that it became politically/economically expedient for certain cities to break with specific federal laws. There's certainly a history of states resisting conformation to federal legal pressure, and it's dysfunctional in the short term, but it's an important mechanism to maintain and grow the system.

Regarding the actual post, I just wanted to mention that the marriage sanctuary city wouldn't work because they would get sued into submission. It's a lot easier to punch up at one thing (individual vs marriage sanctuary city) than to punch down at a bunch of things simultaneously (federal government vs sanctuary cities, weed states, etc.)