Board Thread:Theories and Speculation/@comment-31099706-20170510101001/@comment-734582-20170510102320

Judging by the implied backstory, Momoshiki and Kinshiki were basically representatives of the Otsutsuki homeworld, who came to collect the fruit that Kaguya was supposed to guard but in stead ate.

On that homeworld, the power of at least one whole fruit was present but spread over several people. Since there's no reason to assume the Shinobi world is the only world, it's probable that she would have to fight several fruits worth of power, plus a whole army of Otsutsuki.

Hence, the army. She would be able to project force over a greater area, possibly to force Fruit Users to divert to other worlds to protect them while Kaguya could hold off individual users more easily.