It's that, but it's also that relative to the 80's and 90's, America has gotten less racist (actually and symbolically). It's a very low bar, but it's always shocking looking at media from those times and seeing the shit people used to not even bat an eyelid at on TV. A time before widespread bodycam use (yes, I know, there's still a lot of dodgy bodycam business), before every citizen had a camera in their pocket, before the news would spread like wildfire on the internet, or a video of some professor saying the N word, or whatever.

America is an incredibly racist place, and the system - laws, media, whatever - has undoubtedly done their best to dismantle black radicalism, but America has also got to a point where it is less justifiable than it was to have an armed militia in the name of civil rights. The police are bad now, but they used to be magnitudes worse.

It's the same reason we don't have radicalism in general anymore - the usual factors like repression and surveillance, but also because many of us have our needs just about sated, and have the illusion of free speech. Conditions necessitate militia style resistance - the conditions currently do not necessitate such a thing (to the wider population).

As soon as the imperial profit tap runs dry, living conditions will go down, people rise up - as soon as the state represses them as severely as they used to, the time of militias will be born again.