Downloading for Translation
Downloading for translation is like dining with Pirana - within minutes the document swarms with competitors, making it impossible to translate any large part of the document.
It's really quite annoying to spend many minutes translating a 60 to 90 word sentence and then only get one point since somebody else jumped ahead to do its slightly sooner.
It's also annoying that so few Wikipedia articles can pass Duolingo's various barriers to download - length, improbable possibilities of offense, and others utterly mysterious.
I believe you erred in your description. You seem to be referring to uploading rather than downloading. Anyway, you can also upload a huge article, and most people will leave it alone for a long time.
Those barriers are there to ensure that duolingo can be used by most users, including children, and also to make the content easier to manage.
But how likely is it that a Wikipedia article on Volcanos or Cuban History is actually offensive? I frequently get "document too long" messages. Example: Wikipedia article on Cuba