What do you mean by "that?" I read @AyyashElmota's comment and took it to mean that (s)he was asking why it cannot be in the present indicative construction, as opposed to the imperative.
Also, it may be unnatural in English, but it is not so in Italian (and in Portuguese). Think of it as "You make a good [cup of] coffee," except in Italian you can omit «tazza» and just refer to only the coffee.
This lesson is about imperatives in Italian, not about articles in English. Here is the translation for down-voters:
Actually here the exclamation mark does suggest an imperative, but I understand the frustration. Anyway report it and you will see that sooner or later they will accept it.
«fai»/«fa'»/«fa» is the imperative for the second-person singular, but «fate» is the imperative for the second-person plural: http://www.italian-verbs.com/italian-verbs/conjugation.php?verbo=fare
In Romance languages, "to do" and "to make" are one verb. In English, they are two, and they are not interchangeable. Therefore, you "make" coffee, and you do not "do" coffee. Anything that involves some kind of creation/process, especially cooking/baking, takes the verb "make." Anything that involves some kind of completion/process takes the verb "do," like homework or any kind of task. Perhaps an exception would be to "make the bed."
They want to make it obvious that this is the imperative lesson. Because some of the conjugations in the imperative mood do not change from the present indicative in Italian (e.g. «scriviamo» is both "we write" in present and "let's write" in imperative), the exclamation point tells you that Duolingo expects you to write the answer in the imperative mood.
The imperative (l'imperativo) is used to give orders, advice, and exhortations.
Examples: Spiegaci!, = Explain to us!, Girati! = Turn around!, Non tormentarmi = Don't torment me!, Sbrigati = Hurry up!, Chiamami! = Call me!, Scrivimi! = Write me!, Sta' zitto! = Shut up!, Lasciami in pace. = Leave me alone., Mettila dietro. (una bici) = Put it in the back. (a bike), Non dirmelo! = Don't tell me!, Non fare l'innocente. = Don't play innocent., Divertiti! = Enjoy yourself!, Dille di riprendersi. = Tell her to get better., Non preoccuparti. = Don't worry yourself., Calmati! = Calm down!
imperativo presente [fare] = present imperative [to do, to make]
fài, fa' [non fàre] (tu) .......... make [don't make] (informal, singular)
fàccia (egli) .......... make (formal, singular)
facciàmo (noi) .......... let's make
fàte (voi) .......... make (informal, plural)
fàcciano (essi) .......... make (formal, plural)