Because they have not yet been Genetically Modified yet as we were in the past. Give it a few more thousand years... And they will.
So the "few more thousand years" have passed.
Still no sign of Chimp learning how to control fire, cook, develop art or doing anything but screeching, throwing poo and copulating with any female they can get to hold still. Something like Anti-fa now that I think of it.
Genetically modified by whom?