Roseanne is CANCELED

http://money.cnn.com/2018/05/29/media/abc-disney-roseanne-barr/index.html

As we all know, Roseanne Barr has issued a tweet in regard to Valerie Jarrett in which she compared her to an ape. From what I gathered in the articles that I have read that Roseanne has always been racist. ABC cancelled Roseanne which lead people to ask how they got back in business with her in the first place. Her ex-husband Tom Arnold has issued a statement saying that she has always been this way. Also, her ex said that she is mentally ill. This leads me to ask two questions:

Being mentally ill, does this excuse someone from being racist?

and if ABC knew Roseanne was racist, why would they reboot her show?