This one told me I had the wrong answer when I wrote the exact same thing as the translation above except I didn't put the coma.
Yes, it may be a reason, another excepted version is " Jíme, protože jsme hladoví (hladové)
Check your answer again. DL usually ignores punctuation, so it is unlikely it cares whether you had a comma or not.
Why is Jime protoze jsme hlad. Unacceptable
jsme hlad = we are hunger
máme hlad = we are hungry