this is a ridiculous article, as though citing a couple of people can be extrapolated to an entire subculture.
it is true that these radical black movements were shut down by force, with prominent leaders being assassinated or jailed. but, it's also true that they were broadly unsuccessful in generating any sort of critical mass.
the reality is that black voters looked at the black panthers, and looked at the church, and picked the church over the black panthers.
sanders does get a few black people to vote for him - about 10-15%, in most places. further, they skew younger, which would help him in the 2032 election cycle - and while nobody should be surprised if he at least tries this again in 2024, we can rule out 2032 pretty effectively.
the reality is that that 10-15% is just about the maximum reach you're going to get from this black left today, and was about the maximum reach you were going to get from it in the 60s. it's never been more than that, and fantasies to the contrary are just a type of historical revisionism.
activists can often shout louder than silent majorities. but, the data has never upheld the urban legend of the black left. it's just another 60s counterculture myth erected by revisionists in the 90s.