This is just my two cents, so take it for what it is worth.
Texlonghorn75 is mostly right. Social studies is so poorly taught, and it does not take a rocket scientist to figure out why. I do agree, however, that it is not fair to lump every coach together, as BE said, because some coaches do try to teach their subject. BE is probably an excellent social studies teacher, and I think that everyone should thank him slightly less than military and police officers because it is that important.
Let's take the emotions out of it and talk about big 6A schools. What they do is hire a teacher or two at every grade-level, that teacher tells the coaches what to do, and the coaches execute with varying success. 6A football and sports in general is very competitive, so they will keep an employee if he/she/it is the best X position coach in the State of Texas yet does not know the different between the Articles of Confederation and the Constitution.
Looking at from the coaches perspective, they are asked to do two jobs, and trust me coaching is more than a forty hour a week job, while still maintaining time for a personal life. Thus, I really agree with BE that blaming the coach is not the answer.
The question that interests me is not beating up on the coaches, but who decided that all of them, with a few exceptions, should teach social studies and administrators and society in general would give them a pass? I am sure the other subjects are important as well, but, in our current political climate, ignorance about the past is on full display on both sides.
While I agree more with the policies of one side rather than the other, I am going to refrain from being political in this post. In my opinion, laymen Americans needs to know who the United States got its independence from via the American Revolution or why the United States defeated the Soviet Union during the Cold War rather than know that Act 2 Scene 2 of Hamlet is a play within a play, how to balance a chemical equation, or factor an exponent. Although those are important skills, our country is suffering from a crisis in terms of understanding the past.
I am not a big fan of beating up on coaches because they have it rough no matter what subject they teach. Regardless, society, as a whole, needs to demand more social studies knowledge or we face the risk of making major mistakes that have already been tried and failed historically.
I could ramble about this forever because I am really passionate about it. If any coaches ever want help with social studies, I am here for you. It's a hard job, and I think everyone has put a big burden on them.