It's been strangled by p.c. egalitarianism. The reason is the resilience of racial differences in IQ in the data, perhaps most definitively proven by UC Berkeley psychologist Arthur Jensen:
"Jensen is still greatly respected by many traditional intelligence researchers," Garlick says. "By 'traditional intelligence researchers,' I mean researchers who still value IQ and continue to do studies that evaluate the effectiveness of IQ in predicting outcomes, or studies that examine possible mechanisms that may cause differences in IQ. However, due to the unpopularity of Jensen’s findings, this group of researchers is now very small.
"The major move in response to Jensen’s findings hasn’t been rigorous and compelling research to try and disprove his hypotheses and findings. Rather, it has led to an exodus of researchers away from the area, and a drying up of grant funding and research positions for researchers interested in IQ."
The right response to unsettling data is to probe, experiment and attempt to disprove them – not to run away in racial panic. But the deeper problem is that the racial aspects of IQ have prevented non-racial research into intelligence, and how best to encourage, study and understand it.