I believe the intent here is to show us how to shout out "we can't hear you!", and that we wouldn't use poder (i.e., ¡No podemos oírte!) for this.
Otherwise, there isn't any good reason not to accept "we don't hear you" or "we didn't hear you," or even "we aren't hearing you."
Yeah, but what evidence in the Spanish sentence supports such a conclusion?
Just the exclamation points, which clearly show this is an exclamatory statement. Of course, one could exclaim just about anything. The statement "we can't hear you" seems a natural for using "poder," but I've seen a few examples on Duo with the present tense that don't use "poder," even though we'd include it or a "helper" verb in English.
What David says makes sense. Often logic is good evidence.
For example, say a politician says one thing on the first day, and then the next day says he did not say that. This is good evidence the politician is a liar, or maybe is simply crazy.
A defender of that politician would say you don't have any evidence to draw that conclusion.
True, but in the sentence above, there is no "ahora" or "ayer" so DL ought to accept both present and past translations.