It's because of the stereotyping of Millwall factor. The truth doesn't fit with the desired narrative of wanting to call us out as racists etc. I think Phil and Trevor Lee made us possibly the first League club to play 2 coloured players. Hence the Media swerve it. To both their credit, I don't recall any mention of Racism of any kind from them
I think the big thing that never gets mentioned is that at that time, it was a hell of a lot more commonplace to hear racist remarks in the stands. It was a reflection of society at the time and not limited to just one club.
Phil Walker did say he used to hear opposition players getting racially abused by Millwall supporters, but they wouldn't give any out to him.