Carmel can only exist as an exception within a wider metro area. Once too many communities try to follow it's model, the model no longer works since there aren't enough rich folks to segregate from the poor folks.

It's really not that interesting of a development model to me. These places exist in nearly every midtier NFL city I've been to - one suburb/exurb that is exceedingly exclusive and everyone knows as the "fancy area" of town. One existed where I grew up, and they were ruthless in their "not investing in poverty" stances. What I remember them most for is blocking many public transit projects from moving forward since it would bring the wrong type of folks through their part of town. That single community caused more hardship and pain than any other for the entire metro area, and that will be their legacy to me.

Basically these communities can only exist as minority communities as the model of "only cater to rich people" is simply not sustainable at a wider scale.

Yes, fixing only the easy problems seems like a practical way to go if I were a mayor of a random midwest exurb. It certainly isn't doing a good job or doing anything interesting for humanity though - it's simply doing the obvious most directly actionable thing you could do: make the undesirables someone else's problem.