The stereotypes that proved accurate were often ones which people, for political reasons, wished to be inaccurate. Finding or quoting evidence that supported the stereotype was likely to be career suicide. By contrast insisting that the stereotype was wrong was not.
A simple example will demonstrate this. There is a stereotype that blacks are stupid. In fact on IQ scores, the average black scores in the bottom quartile of whites. (See https://www.brookings.edu/articles/the-black-white-test-scor... for a reference.) The traditional response is to criticize the IQ test as racist, and not to accept that there might be merit to the stereotype.
This is not to say that there aren't very smart blacks - very few whites are as intelligent as blacks like Neil deGrasse Tyson or Barack Obama. But according to the data, the average black is significantly less intelligent than the average white.
Now imagine your average progressive leaning social sciences department. You can guess the reaction to anyone saying, "According to the data we should expect the average black that we encounter to be unintelligent." Data notwithstanding, the reaction will be much better if you say, "There is no evidence for the widespread bigoted opinion that blacks are stupid." So people say the second thing, and avoid the first.