Why do people think all animals are vegan?

I'm vegetarian and I would never deny my cats meat. Trying to make carnivore animals vegetarian is actually animal abuse.

"many people" ... you mean that one idiot that you saw on youtube?

Dogs need 1/3 of their food to be meat protein.

Cats need 100% meat protein.

People who try to make their animals vegan are harming their animals. They are more attached to their ideaology about diet than they are attached to the welfare of their pets.  

Wrong choice in my opinion.  If you aren't going to be a good pet-owner, you shouldn't have pets.

It's a tiny, tiny minority of people who think that. Anyone with a reasonable vocabulary and common sense knows that humans are the only animals that can be vegan: a vegan is an omnivore who chooses to consume no animal products at all.

You are mistaken, “many people” do not “make their animals be vegan” (no one can do that) but a tiny few seem to feed their pets a vegan diet. I guess that's because of ignorance and the idea that animals are toys.

Ask vegans how many Vegan lions they have ever seen.