Anarcho-Capitalism is not ideologically representative of the Black Panters.
Like. At all.
We Want An End To The Robbery
By The Capitalists Of Our Black Community.
That's point number three of the Ten-Points Program, a manifesto written by Black Panther founders Huey Newton and Bobby Seale. I don't know how much more direct you can make it.
The Black Panthers were Marxists, students of a school of conflict sociology. AnCaps and other neoliberals will characterize an essential conflict in government vs. private interest, but that is not, precisely, fundamental to the Marxist conceit. Rather, the essential conflict is class based, with capitalism being the most recent development in exploitation. For Marxists like the Black Panthers, racism is not just some kind of hateful whimsy that only becomes violently destructive when the government jackboots get in on it. Rather, it is itself a product of capitalist self-interest.
You've heard of how "workers must seize the means of production," right? In chattel slavery, such as was practiced in the American South, the workers are indistinguishable from the means of production; they're owned as property in exactly the same commodified manner as a plantation field or a cotton 'gin. Racist exclusion was no less useful for maintaining an exploitable underclass after the civil war, either. For example, the prisoner leasing programs provided slaves-in-all-but-name as a direct byproduct of racist belligerence among law enforcement. The draft during the Vietnam War press-ganged thousands of young men to fight the enemies of capitalism, but passed over people who were in university, which, generally speaking, did not include a lot of black people. Finally, because obviously there are also plenty of working-class white people, racism is a method of division which foils any effective anti-capitalist sentiment by stirring up proletariat infighting.
Pursuant to the last point, I'll also note that, as time went on, the Panters curved away from Black Nationalism and into Revolutionary Internationalism. Yes, the Black Panthers were anti-establishment, but not because they were merely laissez-faire. They were anti-establishment because, in their opinion, the establishment in question was a longstanding edifice of capitalist values. The answer, for them, is not to simply open up a power vacuum where that government stood, if it just means that the consolidated power of the bourgeois withstands the move to "anarchy" and starts cutting deals to trade food to people in return for their eternal bondage. That's just a regression. Rather, to the Black Panthers (and other Marxist groups), the answer is solidarity among the exploited class and opposition to the ideologies which created a class disparity, of which racial disparity is only one kind. That doesn't mean you don't have a government. For many, it means you run one.
So, to answer your question:
Why don't black people embrace anarcho-capitalism when it would encourage groups like the Black Panthers?
Because the only way an anarcho-capitalist encourages an actual Black Panther is by provoking him.