That also raises property taxes, making the neighborhood unaffordable and driving them out.

> it's now a more pleasant area to live in.

For new wealthy residents. People who have spent lifetimes there don't want everything to change and have their communities destroyed.

> Yes, they may have to move, but also the places they move to on their current budget may be nicer - because the people who can afford better have moved too.

These are theoretical and very general averages. The actual individuals often do not benefit. Being forced to move is not a mere inconvenience to your theory.