And there are "historically black universities". But if someone even mentioned the idea of a "historically white university", they would get laughed at and immediately branded a racist.
HBUs accept people of all races. And, certainly, no one would argue that Harvard or Yale were NOT historically white, unless they were blind to history.
The intent is different. "historically black universities" were created to give opportunities to disenfranchised people, "historically white universities" are the reasons these other schools exist.
The "H" in "HBCU" is the important part, and everybody already knows what the HWCU's are: everything else.