The long answer is that we cannot include every regional variant of English in this course. We have a limit on the number of translations, and including every one of these would put us above this limit very quickly. Besides, if we start including some of the variants, people would just want more of them. There is also a need to put some restrictions on what is taught. Were we to add "nonstandard" syntax it might just cause confusion for some non-native speakers of English.
Dont worry, I wasn't asking for Duolingo to include regional variants or annoyed at the answer being rejected. Apart from anything else the example I gave would be how to show with just text. I was just suggesting that the confusion might be arising from this trend of English in the UK. (I said south west because that's where most of the people I see very day come from but I understand its a national tendency)
There is the need to be able to distinguish between certain sentences. Duolingo isn't able to distinguish between "He sings on Tuesdays." and "He sings on Tuesdays?", so some people wouldn't learn the difference between "Han synger på tirsdager." and "Synger han på tirsdager?".