Because straight forward language isn't scientific language and lacks precision.
As a pet owner, I find it absolutely ridiculous and insulting that animals intelligence is assumed to be so low. My firsthand experience is that there is a lot more intelligence there than people generally give them credit for, even if science hasn't delineated every single aspect of it yet. As scientists keep confirming these "discoveries", I think the default assumption (and language) should shift to assuming more similarity than differences unless proven otherwise.