In baseball the New York Yankees do this by letting the A's, Red Sox, Texas Rangers, etc. scout and develop the talent and then swooping in to cherry pick Nick Swisher or Johnny Damon or Alex Rodriguez, etc. And the Yankees are just a microcosm of New York City as a whole, which pulls this same d*ck move all the time.
San Francisco suffers disproportionately from this move because San Francisco shares the same cosmopolitan, liberal ethos of NYC, and relatedly, the same demographic of upwardly mobile girls. Phoenix might lose its talent to Miami or L.A., for instance, but San Francisco somehow always loses its talent to the big Apple. The process is not always instant but it's inevitable, which is why whenever we spot a pretty girl on the streets of San Francisco we never really appreciate the moment, we're too busy thinking about the Canadian Football League, and the day it lost Doug Flutie to the NFL.