In English, doesn't "Mom cooks delicious food" imply that "mom cooking delicious food" is something that usually happens? I think so, but I'm not a native speaker. Explicitly including the "usually" here would imply that sometimes she doesn't, I think, which is not implied at all in the Swahili habitual tense.
I hear what you are saying and it probably does imply it. But I'm arguing that adding "usually" shouldnt be a mark against me. All of the test cases say i am wrong for adding 'usually'. In all of the literature that I have found states something similar to the below....... "The "habitual tense" is a variant of the present tense, which means 'usually/usually not'."