Translation:Why do they write or read during lunch?
Take a look at the following link from the BBC:
Lunch does not have an article. I'm not sure which sentences you were talking about that did feature an article, I haven't taken these lessons :)
Look at that:
With commonly used nouns when there is general reference and when they are used with prepositions there is normally no article
NORMALLY, not always. I saw many times correct sentences using "the breakfast" etc. Also on Duolingo in other courses there were used articles before "lunch", "breakfast" or "dinner". It is not incorrect to use it, so in my opinion it should be accepted.