The answer for us is that all the local service providers live far outside the core urban areas and have terrible commutes. Or they double or triple-up, multiple families per unit. As the area becomes increasingly unlivable for people that do the local gruntwork, a number of them leave the metro area. Those that stay have less competition, and so they start charging higher wages. Eventually the local economy equalizes at a much higher price point; local service workers find they make a livable wage again; globalized tech workers find that most of their income is eaten up by daycare, housecleaning, gardening, and restaurant meals out (to say nothing of housing); and the whole region settles into an uneasy truce, yet enjoys great geographic arbitrage opportunities over other regions. We can go make Halifax unaffordable and live like a king there, for example.