Why is Howard University still predominantly black?

I just don't think HBCUs are all that unusual in terms of having a student body that's not a random demographic sample of the United States. Brandeis has a higher than average percentage of Jewish students, Cardiff has a higher than average percentage of Welsh students, and Duke has a higher percentage of southern students. Students pick schools in part by cultural and social match, and ethnicity plays a role there. Furthermore, people go to schools that their family members and friends went to, and a black kid is more likely to have grown up hearing "keep up the good work and you'll get into Howard/Morehouse/Spelman" from their alumni parents and teachers while a white kid's role models are less likely to be Howard alums. Finally, demographic shifts happen slowly: Sarah Lawrence has been coed since 1968 and it's still 3/4s female.

The excellent book "Why Are All the Black Kids Sitting Together in the Cafeteria?", by Beverly Daniel Tatum, offers an explanation of -- well, the question posed by the title of the book, but as a general phenomenon, for example why HBCU's continue to appeal to African-Americans.

As a Black graduate of Howard University, I think this best sums the factors and answers your question. The United States of America, has embedded within its socio-economic and political systems, systemic racism. The reasons for Howard University, in fact all HBCUs existence still remains. Until the systemic racism is directed to all OR until it is significantly removed, there is no reason for any HBCU to become a PWI (predominately white institution).