It's not that Americans are less knowledgeable about it now than ever before. It's a general lack of education about these things which is comparable to similar data from previous decades. Someone pointed out on Twitter that the number was 17% in 1994, which is roughly on par with 11% now.
It's still incredibly sad that millions of Americans don't know about the Holocaust when people who suffered because of it are still ALIVE today. I think the concern is legitimate that as the remaining survivors die, people will know of the horrors of the Holocaust less and less. We all have a responsibility to make sure that doesn't happen.
Unfortunately, I think a kind of "knowledge slip" is largely inevitable, because it's the kind of thing that happens to countless events over time. Once something enters the realms of relatively distant history (defined as nobody alive remembering it), there's a tendency to file it away. I'm not sure how we stop the effect itself from occurring, but I obviously agree that there's a necessity in preserving information and accounts while there are still living survivors.
