It's slowly getting better, but medical care is lagging because doctors are way more likely to be old.
It's "implicit bias along ingroup".
Those old white doctors never grew up socializing or even really seeing Black people as toddlers.
So they're not good at reading emotion (in this case pain) in Black people.
Low melanin makes everything easier. Pupil dilation, blushing reaction, all these things we look at on a subconscious level to understand what another person is going through is just more visible with less melanin. So if you only grow up with low melanin people, you're never going to learn to look deeper.
We can use conscious thinking to combat that, but as you age and lose critical thinking, the problem gets worse again. So a 65 year old white doctor just isn't capable anymore of doing that. Rather than understand the science behind it, they double down and say if they don't think a patient is really in pain, they're lying to get pills.
It's like how when surgeons were told to wash their hands for their patients health, more stopped washing their hands than started. The medical community even got the doctor who publicized washing their hands committed to an insane asylum.
Elderly people usually respond with aggression when their knowledge or skill is questioned, which ironically is another sign of the age related mental decline they claim isn't happening to them...