Why do we talk?

[Esaman]

We talk because we're able to.

Nope, there is generally motivation, function, purpose behind such things even if one is not aware of why he is doing it.

You could ask "Why are we able to talk?" Which is also an incredibly simple answer; "It was once evolutionarily advantageous to develop effcient communication."

Yes, but the question likely assumes that and detail on why is it advantageous is asked for.

Sure, exchange of perspectives on value of things for expanding and improving ones own is one of reasons of talking.