A person doesn’t become an indoctrinated cult member overnight. It is a gradual process.
Similarly, many groups did not become a cult (a group that employs mind-control aka undue influence) instantly or even purposely. They evolved from a fringe movement into a high control group over time. The group semiconsciously does what it needs to do to perpetuate itself…those fringe groups that did not evolve withered away into obscurity.
For instance, whatever happened to Barbour’s group after Russell split off from him? Does his group still exist? If it does, it is very very small.
Of course, had not WWI happened in 1914, the Bible Students would’ve had a similar fate. Even then, the Watchtower would’ve likely remained an obscure group, like the present Bible Students, if Rutherford had not taken tyrannical control and gradually creating a centralized top-down organization.