When the "Sanctuary Cities" movement began, the rationale offered for doing so was that city police forces wanted the policy. The argument being illegal immigrants would cooperate with police if, and only if, they were sure they wouldn't be turned over to "la Migra" for deportation.
Oddly enough, we have very little evidence that policy ever worked. We have plenty of evidence that criminal immigrants, left here by police not cooperating with federal immigration, have engaged in lots of further crime, including multiple murders.
Clearly, police wanting it wasn't the only motive for declaring sanctuary status. There was also plenty of low-cost virtue signaling going on. "Look at us, aren't we big time humanitarians?"
Border state governors forwarding the new arrivals to these would-be sanctuaries was one of the smartest things ever done. Now big city dwellers far from the border are footing the bill, dealing with the difficulties, and not loving it even a little.
Even Joe Biden is feeling the heat as big city mayors, all of them Democrats, publicly say "Enough." Wouldn't you bet they say a lot more privately?
Thank TX Gov. Abbot and FL Gov. DeSantis for figuring out how to move the argument over illegal immigrants away from between the parties and make it instead happen within the Democrat Party. I'd call that world-class political judo.