Well, before we can discuss the "answers" the first step is to come up with an algorithm that measures how much a given piece of civics knowledge pays rent. Is it useful to know the nominal structure of the government (vs the 'actual' structure in practice)? Is it useful to know the retold tales of George Washington, victorious general and American hero? (not to mention the high probability of errors in the 'knowledge' given the time that has passed and the likely bias)
A reasonable argument could be made that in our form of democracy, civics knowledge is of little use to the average citizen. This is because that each of us has such an infinitesimal 'vote', and each person well educated in civics has their vote drowned out. If 1 in 1000 citizens are genuinely well educated in civics, and nearly all elections are decided by a margin greater than 0.1% (or this is below the noise floor for the voting machinery itself...), civics knowledge is useless.
If this hypothesis is true (not saying it is or isn't), the culprit would be a failure of colleges and others to be accountable to a measurable cost/benefit ratio for the things that they teach. Instead of using measurable metrics they use arguments like "this knowledge is clearly worth it because of what it is" or "tradition says we have to keep teaching it".
This is one reason why we all had to waste some of our lifespan on trigonometry and literature instead of say learning to use Python more effectively. Arguably knowing how to tell a machine to do your math for you effectively is thousands of times more valuable than useless derivations you won't need to know unless you become a mathematician.