What incentive would local governments have to find a niche? I don't see how there are more votes in attracting childless professionals vs poor families.
If you take from the middle class to give to the poor and the next city over doesn't, those middle class people vote with their feet, and then you no longer have that money to spend on anything, and your remaining constituents are upset with you when the drop in revenue necessitates a drop in spending.
Which is ostensibly what the majority in that city wanted, because they voted for officials who set things up that way. And then once that happens, the people who want things that way (i.e. the middle class) from other cities move to that city, and the people who don't (the poor) leave for some other place, which bolsters popular support in that city for things remaining the way they are.