Have any morris dancers done much dancing in those areas, black-faced or not? No? I wonder why that might be…

Performers of any description have no real knowledge of the exact make-up of the crowds in which they'll be performing in front of. Plenty of black-faced morris dancers will have danced in front of black people if they have danced in the city-centres of any large or medium-sized British city. To hint - as I believe you are doing - that cowardice is the reason behind the lack of morris teams performing in the more notorious areas of the UK with large black populations is just wrong. I lack of interest/opportunity if much, much more likely to be the reason, speaking as someone who has lived in Tottenham and on the Meadows estate and Radford in Nottingham.