You keep conflating what
should happen with what
is happening.
You're operating under the unprovable assumption, unprovable both numerically and specifically, that race isn't a factor in how NFL coaches are hired. We do not have a perfect way of knowing how much race factors into NFL coach hiring practices. Wishing it was working fine does not make it so.
Although far from perfect, the only way we can try to measure it is by analyzing three things:
- Comparing the percentage of coaches by race versus the percentage of general population by race and
- Analyzing the systems in place for hiring.
- Analyzing the level of interest by race (or by other demographics, if pertinent).
You must do all three things or we're only looking at a partial picture. If the system in place (#2) can be determined to be both rigorous and unbiased with respect to race, then it should take priority over the comparison of percentages. Doesn't mean #1 goes away entirely, but it means it's far less likely that race is a determinant.
#3 is necessary because not all races among the general population have the same level of interest in a job in the NFL. There might be N Indian-Americans in the US, but a poll of Indian-Americans will likely reveal that interest in coaching in the NFL is considerably lower than, say, among white or black Americans. That is a mitigating factor when considering item #1 from above.
If there is no #2, then all we have is #1 (possibly mitigated by #3). And that's the current situation with NFL coach hires. And at the moment, to choose one race, black head coaches in the NFL comprise about half the percentage of black people in the general population. And interest in football and coaching among black Americans is as high as any other high-interest ethnic group in America, so there's no mitigating factor to explain the percentage gap.
So the fact that there are, and have been, so few black NFL head coaches is inexplicable and thus troubling to people who value diversity. For those who dislike diversity, or dislike one or more races, it's not troubling in the slightest - it's a good thing. And thus they will speak out, in various ways, always in opposition to diversity.