The problem is that people don’t usually select their mate based on intelligence. This includes “the rich” as well as “The Poor”.
This may enlighten:
https://www.youtube.com/watch?v=_BKPgI5lw_Q
BTW, I was basically parroting information I got from an article in Scientific American about 30 years ago. It was comparing sex with cloning and had a funny picture of “obviously dumb as a box of hammers” parents beaming over their daughter singing and dancing in her crib.
This used to be the case.
Until quite recently in historical time, there were far more intelligent people than occupations in which their intelligence was needed or even particularly rewarded. Thus for most of human history there have been large numbers of highly intelligent slaves, serfs, peasants, etc. In such occupations high intelligence may often have been a handicap, leading to inappropriate behavior punished by the power that be.
High status in society was determined more by birth than by competence. Thus there were many high status but dumb people, and lots of smart but low-status people. People associated closely with, and married and had children with, people of widely varying IQs.
This situation has completely reversed. The only occupations in which there is more demand than supply are those requiring high intelligence.
Male doctors and lawyers associate mostly with female doctors and lawyers and are much more likely to marry them than in the past, when they tended to marry secretaries, etc. This was of course because there were very few female doctors and lawyers.
IOW, this country is largely sorting itself out by status, and therefore in a rough way by intelligence, and people mostly marry within these groups.
Not entirely a positive development, IMO, but one that cannot be stopped in a free society.
This was all covered in the Bell Curve 20 years ago, and the trends they discussed have only increased since then.