Maybe that's because Marxism has never been a football related issue - until Black Lives Matter came along. The leading figures in that organisation are anti capitalist political activists. They advocate defunding the police , compensating black people for historical slavery ,defacing statues of people like Winston Churchill. Research their views and objectives -Joshua Virasami and Sasha Johnson - if you don't believe it. If you want to support those sort of characters that's upto you - but I won't be taking the knee for them nor do I want the football team I support doing it either.