They just don't get it. Years ago, I worked with a young white dude from Northeast Philly. Nice enough and smart enough, but everything in his mannerisms projected that he should have been doing construction work instead of having a white collar job. Me and two other co-workers constantly schooled him on how to present himself better. And to his credit, he listened and learned.
My immigrant ex-wife tells new immigrants to learn how to act like white men because that is the culture of business.
I'm sorry, but if you show up at an interview with me with your pants down below your a**, you will get five minutes and a trip out the door. And if you are white with your a** hanging out of your pants, you won't even get that five minutes.
My wife is a manager for a large concern and occasionally has to hire workers. She interviewed one young, white woman a few weeks ago for a position. During the interview, the young interviewee's cell phone rang. She hadn't bothered to turn it off for the interview. And then she took the phone out of her purse, and answered the call. She was on the phone for several minutes while my wife watched with mounting anger. The young white woman did not get the job.
It is true that if you want to define "blackness" as a poor attitude and a paranoia that everybody is against blacks, yes, others will not want to work with you because the tension and drama is distracting.
Every group has norms that they want observed. If you constantly remind everyone by your behavior that you don't want to be part of their group, they will shun you.
Some groups are easy to blend into, others just aren't a good fit for you so you move on. It happens to all of us.