Concepts are internal representations in the brain of outside referents in the world.
Concepts are the second link in the language chain. Originally they occur as a direct result of stimulation. They are basically the brain's record of our contacts with reality.
Sometimes they are sparse and/or concrete (like our recognition of a pebble); but they can become abstract and involved (like our knowledge of superman).
If there is one thing we, as a species excel in, it is storing these bits of information in great volume.
Our recognition of countless items (from specks to planets) in our environment is a testimony to our awesome capacity to store concepts.
As amazing as some other primates are in their intelligence, they are no better at storing concepts than most of us are at swinging through the trees.
This alone for them would be a severely limiting factor, by human standards, for language development and its use as an communication bridge.