There is not 3000 _core_ words. You don't teach elementary school children 3000 words. That list is significanly smaller. In Denmark it's 120 words, then you'll be well on your way to reading and writing most basic stuff.
That someone has selected 2048 words used to generate passphrases, doesn't make it easy to remember.
Eh, you may want to peek at the XKCD things explainer to see what is life under 1k words.
Everybody uses more than a few thousand words on at least one language. And selecting the least used ones will make your passprhases easier to memorize, because they have much more concrete meaning (by virtue of their rarity) than the most used words.
I've been doing this for years and it is indeed easier to remember. You won't be keeping all your passwords in your head in any format if you're using a unique password per site or service as you should. But you occasionally have to buffer them mentally between your password manager and the input box (especially on mobile), and the same number of bits of entropy are infinitely easier to copy correctly in this format vs something like "?G[G6n|4".
Err.. I would suspect most(non-english?) people on the internet to know 2000 words. (By virtue of being atleast bi-lingual, they would, so the challenge boils down to can they type it? unicode support should help, but I've found most cases people simply type those sounds in English.)
As for the English as a primary language people, I've no clue about the number of words, but if we can expect them to type 1024 words, we'd still get 20 bits..
Here's Merriam-Websters 3000 _core_ words [1]. Here's a list of 355k words [2].
[1] http://learnersdictionary.com/3000-words
[2] https://github.com/dwyl/english-words