That's because beavers don't speak English.
> it doesn't have a greater plan of building a dam, etc.
Just because you've never seen beavers with little tiny HP calculators poring over pages of drawings and equations does not mean that beavers are mindlessly purposelessly building the dams. You think they just throw stick and through some coincidence, a beaver lodge appears? That's crazy. Beavers build those dams with the intent that it will protect them from predators; they intend to dam up creeks in order to submerge the eventual entrance to their lodge. It is deliberate.
Source?
Beavers are best known for their dam-building. They maintain their pond-habitat by reacting quickly to the sound of running water, and damming it up with tree branches and mud. Early ecologists believed that this dam-building was an amazing feat of architectural planning, indicative of the beaver's high intellect. This theory was tested when a recording of running water was played in a field near a beaver pond. Despite the fact that it was on dry land, the beaver covered the tape player with branches and mud.
-- Richard P.B. (1983). "Mechanisms and adaptation in the constructive behaviour of the beaver (C. fiber L.)". Acta Zoologica Fennica 174: 105–108.
>as soon as they had comfortably bestowed Sandy and me on our horse, I lit my pipe. When the first blast of smoke shot out through the bars of my helmet, all those people broke for the woods, and Sandy went over backwards and struck the ground with a dull thud. They thought I was one of those fire-belching dragons they had heard so much about from knights and other professional liars. I had infinite trouble to persuade those people to venture back within explaining distance. Then I told them that this was only a bit of enchantment which would work harm to none but my enemies. And I promised, with my hand on my heart, that if all who felt no enmity toward me would come forward and pass before me they should see that only those who remained behind would be struck dead. The procession moved with a good deal of promptness. There were no casualties to report, for nobody had curiosity enough to remain behind to see what would happen. --Mark Twain, A CONNECTICUT YANKEE IN KING ARTHUR'S COURT
GP can reason about what he's doing. He knows that he's commenting on HN. He can come up with a plausible reason why (recreation, perhaps). In a more interesting scenario, say building a dam, GP would cut down logs with the express intention of building a dam to make a pond.
The beaver doesn't know what it's doing, literally. It can't tell you why, it doesn't have a greater plan of building a dam, etc.
You're really talking about motivation, and I'll agree that the motivation is roughly the same for GP and the beaver--some mix of chemicals in their respective brains influencing behavior.