Because White capital invested in them (namely Chinese Americans) during WW II, a diplomatic gesture as they were trying to make allies against Japan.
At the time of the 1940 census, Hilger found, California-born Asian men earned less than California-born black men. By the 1970 census, they were earning about the same as white men, and by the 1980 census, the native-born Asian men were out-earning white men.
Throughout this time, many Asian American families did invest, increasingly, in their children's education. But Hilger discovered that the improvements in educational attainment were too modest to explain how Asians' earnings grew so fast.
The picture became much clearer when he compared people with similar levels of education. Hilger found that in the 1940s, Asian men were paid less than white men with the same amount of schooling. But by the 1980s, that gap had mostly disappeared.
“Asians used to be paid like blacks,” Hilger said. “But between 1940 and 1970, they started to get paid like whites.” The charts below shows average earnings for native-born black, white and Asian depending on how much education they had.
From article:
The real secret to Asian American success was not education