Before the invention of the pokeball, there were many different tools used for controlling domestic pokemon, none more ubiquitous than the collar and manacles. Initially used on ferocious, untamed pokemon such as the Granbull of that age, their ease of use and effectiveness saw them extended bit by bit to nearly all pokemon they could be fit around, and eventually even to human slaves. Their impact on the psyche was much like that of a pokeball, but where a pokeball produces loyalty, the collars produced only docility and a broken spirit. It was this age from which Team Plasma took their inspiration; had they been founded in those ancient and brutal days, they might actually have had a point.
The collars of modern Granbull are a legacy of that awful era. Early Granbull evolved from Snubbull who either neglected their responsibilities in order to pick fights from wild pokemon, or from Snubbull who accompanied their trainers on the hunt; both types were too proud to be treated as a mere domestic pokemon. And so they were shackled, and manacled, with stronger shackles each generation, removed less and less often as they rebelled and time went by. And in some twisted, Lamarckian nightmare, they began to evolve not into proud beasts, but into slaves who can never be freed, for their binds have become part of their body.
It is not needed to weep for modern Granbull, for the collar is lighter every generation since they have gained the half-freedom of the pokeball. They have always had the strength to battle through their bonds, although they can not simply drop the weights like so many heroes of martial arts anime. But until the day comes where their bodies are free, we are right to remember the cruelty of our ancestors.