I was watching my dog licking my plate on the floor when it keep sliding away. I said Fisher, put your paw on the plate and it won’t slide away.
Of course he doesn’t do that and the plate keeps sliding away. That made me think, why are animals so dumb?
Because they don’t need to be smarter. They have successfully evolved to the state they are in at their present average intelligence level.
We actually breed dogs to weed out or support certain characteristics. Had we targeted paw/plate coordination as a desirable characteristic then you might just be seeing some dog breeds who have a tendency to do that.
Dogs in the wild don’t often eat off plates, so there’s no reason to develop the skill.
My dog gets free room and board and has her own servant to pick up her waste. Who’s so dumb?
My German Shorthair would bring me his food bowl when he wanted food put in it.
I have had a couple of dogs that, when their water bowl was empty, would sit in front of the kitchen sink and stare up at the faucet. I thought that was pretty clever of them to figure out that was where their water came from.
Intelligence takes energy. Having more than you need is bad. Have you watched a human child grow up and learn how to do simple jig-saw puzzles? First they try to eat the pieces, then they learn to figure out where a piece should go, but they are remarkably resistant to the idea that the orientation of the piece matters.
Some dogs would, due to previous experience and innate smarts figure out what you’re expecting of your dog, but yours evidently lacks previous experience with relevant environments or smarts or both.
It seems to me that that explains the dog’s lack of instinct but not his lack of intelligence.
As lovable as I’m sure your dog is, I think it may be YOUR dog that is less than brilliant. 
Most dogs I’ve come across know to paw the plate.
Cats however, don’t. Which is ironic considering they are the smarter of the two species.*
*Smarter if you are using number of synaptic pathways to determine intelligence.
The more interesting question IMHO is “Why are humans so smart?”
After seeing mama ducks lead their ducklings across busy streets and prarie dogs hiding under cars at stop lights I’ve often wondered the same thing.
I guess they don’t need to be that smart for some of them to reproduce and its a natural-ish form of population control.
I realize my dog is a dumb mutt but hey, I love the little guy. 
What’s dumb about that? The dog successfully got the food into its mouth. The fact that the plate slid around is irrelevant to the dog. Keeping it still is only infinitesimally more efficient, and slightly more polite to delicate human sensibilities.
In the wild, the dog’s ancestors were plenty successful at finding food and keeping it still long enough to eat…
Intelligence is highly overrated as an evolutionary advantage, mainly because it’s our own major claim to superiority. Millions and millions of animals do perfectly well with brains smaller than a pea.
This is like a cheetah asking why other animals are so slow or a giraffe asking why they are so short.
A lot of animals are pretty dumb at doing human things, but they’re pretty damned “smart” at what they need to do to survive and propagate. (Likely exception for domesticated species.)
At the risk of anthropomorphizing (sp?), if you had to live for a day as a dog, I can imagine a lot of dogs wondering why you were so dumb at being a dog.
Why do you think a cat brings you a dead mouse? It’s not a gift, as that’s not how animals operate. It’s trying to show you how to hunt, because it has never seen you do it. If the cat had the same thought processes as humans, it would wonder why humans are so dumb.
Your dog will figure it out, IF said dog wants to.
You’re dog has food brought to him, he has a lot of time on his hands, so pawing the plate isn’t a priority. So instead of taking him 10 minutes to eat dinner, it takes him 20 minutes. He isn’t going anywhere and he knows it.
Put another dog or two trying to get at his food and he’ll quick as spot figure out how to paw it and get it in his mouth before the other two dogs get it.
Because that’s how we get by. We don’t have claws, teeth, agility, or much insulation - but we’ve got honkin’ big brains, and we can damn well figure out how to make our own claws, teeth, cars, and coats. Combine that with our extremely complex language and modes of cooperation, and our smarts enable us to thrive in more environments than any other species.
Ah, you need to test this. For science.