why is it rosto and not cara here?
Thia sentence is poetic XD. cara is too informal and does not sound good here.
so is "rosto" something formal for face then? like this is the first time I see that word
In fact, "rosto" is the correct word. "Cara" is a slang.
so why do you teach cara then?
Because you hear that all the time, and it is really important to learn slangs.
"Cara" also means "dude".