There are a lot of problems with Harris but questioning why Biden chose her is idiotic. The reason is obvious; Biden chose her for the same reason Trump chose Pence. Women and African-Americans are the two largest parts of the Democratic base and Harris checks off those two boxes. White men and evangelicals are the two largest parts of the Republican base and Pence checks off those two boxes. Your vice-presidential pick shouldn't hurt the ticket. Harris doesn't.
More over your post is juvenile in so many ways. Whites don't vote for skin color, they vote for policy. Quit projecting your tribal racial bias's onto white people.