I think wall street has been hiring PhDs to code for a long time. I don't think this is a new phenomenon.
Cornell physics PhDs: 3
Harvard physics PhDs: 2
Princeton physics PhDs: 2
Univ of Penn physics PhD: 1
Other physics PhDs: 2
Cornell applied math PhD: 1
Other applied math PhD: 1
Cornell mechanical engineering PhD: 1
Univ of Chicago finance PhD: 1
So, if by "dropout" you mean that they didn't complete their PhDs, then no, that's wrong. If by "dropout" you mean people leaving physics, then yes, it's very common (especially for theorists -- all physicists on the list above where theorists except maybe one or two).