Poor numbers.
Elephants are a lot smarter than wolves. And panthers (who also have an Int of 3). Cat intelligence is generally considered low based on most research.
Elephants are smarter than baboons, but baboons are Int 4.
Apes have a 6. Elephants are easily near apes and elephants too use tools.
So either apes should be lower, or elephants should be higher.
In the big scheme of things though, the Int listed in the MM is a good enough rule of thumb for DMs to make reasonable decisions. The vast majority of animals who throw things at other creatures in the real world (apes and baboons) have Int 4 or higher. Real world creatures which have Int 3 in the MM almost never throw things at others (elephants being nearly the only exception), hence, neither should the Tarrasque. It is limited to normal animal intelligence, so it shouldn't do things in a game that an animal wouldn't. But, a given DM should feel free to ignore that.