are black people too stupid to get a free id card
No, but poor (black and white) people have less free time to wade through the bureaucratic quagmire surrounding voter registration. Every additional hurdle and unnecessarily verification chops off a certain percent of lower-income voters, most of whom are minorities and Democrats who people like Kobach (Annoying Orange's 'election integrity guy') know will vote against them. It's literally a deliberate move to suppress votes in a democratic society.
Everyday conservatives have been convinced by these politicians that this is something they're doing to make our elections 'fairer' when there is literally zero evidence suggesting we have widespread voter fraud. It's blatantly evil bullstuff wrapped up in a package that looks virtuous.
I am a college student with far more free time than the average adult, and it was still a monstrous pain to register to vote. Throw in those same bureaucratic hurdles plus more, and there's no reason to expect why many people working ten hours a day at minimum wage would have time to navigate that bullstuff.