It does make sense from a practicality point of view. The stones have already been cut and smoothed, and are not in the middle of nowhere as to making transporting them a hassle.

it's nothing new. It's really a wonder that there's anything left of the ancient world at all, since stones have been taken from ancient ruins to build bridges, churches, and roads for as long as people have been building with stone to begin with. But it is a bit unusual to see that in more modern times, especially in cities like San Francisco.