[smacktoward]

The point isn't that they're valid words (you're right, they are), but that they're not commonly used words, and thus come across as formal and somewhat show-off-y. More people will understand a simple, commonly used word than will understand a more complex, less commonly used one, even if it's an exact synonym.

The people who write for governmental agencies tend to be highly educated people, and highly educated people have a bad habit of thinking that if they aren't constantly demonstrating how highly educated they are, someone will come along and take all their certificates away. So they lard their prose down with ten-dollar words, which makes sure that the only thing their readers will come away with is a sense of just how smart they are. (Or think they are, anyway.)

For a writer, the road to hell is paved with thesaurus pages. Use simple words, and anyone with basic literacy will be able to understand you.