It's because WP is an encyclopedia, not a bulletin board. If people aren't literate enough to understand text well-enough to restate it in their own words, do

It's because WP is an encyclopedia, not a bulletin board. If people aren't literate enough to understand text well-enough to restate it in their own words, do you really want them adding that text to WP? It may be obviously wrong, it may be misleading, it may be off-topic or not fit logically into the surrounding text, etc. A copy-pasted "encyclopedia" would be an ugly mess. I frequently find a sentence or paragraph just tipped in somewhere that's in the wrong place. That's a collage, not an article.