Because none of the factors you list explain the difference. There is 100% scientific certainty that there is a genetic basis for the racial IQ divide. This was never a real debate, it was always reality being attacked by ideologues. But modern technology has simply side stepped the ideologues shouting "racist pseudo-science" at facts they don't like. Over a dozen specific genes have been isolated that affect IQ, both positively and negatively. The distribution of these genes in racial groups is as would be expected based on the measured IQs of those racial groups. Many people were conned by the "IQ isn't real it is racist pseudo-science" lie. I do not believe "DNA isn't real it is racist pseudo-science" will be as effective.