Você conhece essa música? (Do you know this song?) / conhecemos ele (we know him) / prazer em conhecer (Nice to meet you) / você sabe essa música? (Do you know this song? - know the lyrics or how to sing it) / não sei cozinhar ( I cant cook / i dont know how to cook)
Because they have elected to teach that variant of English. If you try to learn English from Portuguese you'll see this comment (https://www.duolingo.com/course/en/pt/Learn-English-Online):
Spoken by over 750 million people, English is the second most spoken language in the world (after Mandarin), and the most commonly learned. On Duolingo, you'll learn American English, but you'll be understood in any English-speaking country.
I'm British and very few of my Britishisms are rejected and I only wince occasionally when I read Duolingo's English sentences. :-)