Our society is a meritocracy, yes (with merit mostly measured by IQ). But I’ve started to think that we don’t reward merit/IQ so much as we punish its absence.
Many social institutions were built up to simulate the effects of IQ, binding marriage being one of them. In destroying the ability to legally make a life-long commitment, we eliminated the ability for most of those in the lower class to get the benefits of a life-long marriage. Those will now accrue only to those who are able to maintain the composure not to hit the self-destruct switch for every moment in their entire lives.
This is, in effect, the removal of safety nets. Now, your ability to succeed is driven far more strongly by innate qualities than before. If you lack those, you once could have fallen back on the other institutions built to catch you. Now you just fall.
Picture a rock wall. There are some people who can free-climb all the way to the top. Many more could do so with the help of some ropes, but the free-climbers have cut all of those. If they ran a study, they would find that ability to reach the top really is driven entirely by climbing ability. Tying a rope around your waste is found to have no effect (and nobody realizes that in the old days, ropes had the other end attached to the mountain). So at the top of the cliff, you have a lot of free-climbers strutting about, congratulating themselves on how evolved they are to not use ropes, as their fellow climbers splatter on the canyon floor below.