Professor James Flynn subsequently announced, in Beyond the Flynn Effect, that the reason IQ scores are going up is because people are getting better at IQ tests (no, we’re not getting more intelligent).

One study suggested that somewhere around the 120-mark, or just “above average”, is the sweet spot for career success.

The “gains” listed in the OP are really just another way of saying that having valuable skills offers a means to escape the dangers posed by poverty. You don’t need a high IQ to develop skills, though it can be helpful. What you really need, in abundance, is determination.