> The speech is readily found by those who know how to Google.

Unfortunately, textbook are still a/the standard source of information in most public schools. Yes, this raises separate questions about the way that we structure our education system, but that's not the issue at hand.

The speech is readily found by those willing to go out of their way to look for it, but it is not included in most textbooks, because those publishers would then have to pay royalties to the King estate (and indirectly pass those costs along to the schools).

The video is much harder to find (legally, not illegally!), because the King estate controls it much more tightly.