That may well be correct. Disillusionment drives some of the activists. But I think most are being driven by ideology that teaches them that they are entitled to things without working for them. This are being expertly manipulated and exploited by communist agitators.
You have a good point, but as blacks watch the plight of whites deteriorate they realize there is nothing left for them - they can’t get blood from a stone. Urban areas around me (northern NJ) have lost jobs, and it is hard to provoke class envy when the permanent underclass sees less & less of any other class.