They can afford to demand competence, and they need it. But they don't always get it.
They are the reason it can be hard to hire qualified C++ programmers elsewhere. You compete for the rest who find Wall Street and monopolists both morally repugnant.
I would say programming is really difficult and it is hard to find competent(pick an arbitrary line in the sand) for any skill let alone programming. Pick a field, and the web is stuffed full of people with battle stories of cleaning up after other people. This is actually a point or two against C++ as the breadth of it is so large. The trick, as in any practice, is to find motivated people willing to learn that are not stubborn in their set ways.