When we listen, we learn. When we speak we manipulate. This may sound cynical, but it is actually self-evident. In listening, you may just be learning what the response is to your last order, but you are still learning. In speaking you may just be manipulating the listener into saying things which you want to learn from (like the answers to your intelligent questions), but fundamentally that is what is going on.
Communication allows cooperation - no cooperation can exist without it. Cooperation also allows greater productivity. Two cooperating individuals can often produce more than twice what one could produce. Groups can become greater than the sum of their parts.
Unfortunately communication allows initiation of force against others in the form of collectivism. In a collective, a powerful communicator can gain more through unproductive manipulation than through genuine productivity.
"You should share some of your meat with me this time because I shared with you last time, and back then I gave you far more than you are giving me now, and it was better food, and I gave you all the best cuts, and you are giving me gristle, and the whole tribe can now see how you treat your comrades, and they should just banish you now and let you starve because you aren't pulling your weight, and .. "
In a heavily controlled social situation (like a prehistoric tribe), this could get you far more food that actually hunting it yourself. You didn't have to actually produce anything - you just had to position yourself as a tribal elder. Just like a modern day politician.
Wherever resources are limited, and rule is by the collective, it is far more important to be able to justify your position than to actually produce. Our communicative abilities are largely geared towards that - not actually communicating to produce. Witness unintelligent, and seeming inarticulate people justify themselves when they have done something obviously unjust, and this will become obvious.
While Selfish Gene Theory suggests that such tribes would have died out in favor of more productive ones, the reality is that a strong collective can wipe out a group of individuals because of their greater ability act as a coalition. They can wage war with the neighbouring tribe, and take their resources. Their greatest weakness is their greatest strength. They make poor producers, and good looters.
Hence communication has evolved more for self justification than production. And the people who are in control (the politicians), are often the best communicators of all.