On the girls' side, they mature physically at an earlier age, and the best ones stop USTA play for bigger challenges at an earlier age than on the boys' side, which has an effect on the TRN accuracy at the very top. The examples you cited of very high level girls do not apply to lower-level boys, like those at Morgan State. Amanda McDowell was a 5-star, by the way, who only played enough USTA to get to around #30 her last two years in high school, which is very high 5-star, almost blue chip. She was a blue chip before that (e.g. 10th grade).
I wonder what the Williams sisters and Amanda McDowell have to do with the level of players that Morgan State gets?