We all remember the first time when Luffy and co. visited Sabaody Archipelago. The Straw Hats almost died when they faced the Pacifista. The real Bartholomew Kuma showed up on Sabaody he quickly gets rid of Zoro and then he got rid og PX-1.
The way it’s drawn shows that he got rid of PX-1. So he can take care of the Strawhats himself. But what if, Kuma’s only purpose for coming to Sabaody wasn’t to aid the Strawhats, but to send the PX to the base of the Revolutionary Army? As I already talked about Kuma being a member of the Revolutionary Army before he decided to take part in this human weapon project.
However, we can assume that it’s to get information for the Revolutionaries, which is related to the big projects of the World Government. We already know that Kuma was following the Strawhats because he was ordered to do so by the World Government. But, is possible that he did so out of his own interest.
During this time, Luffy causes a huge problem for his crew which would most likely have destroyed all of them. This causes a great reason for Kuma to enter the fight that took place on the Archipelago. Kuma did this in order to “eliminate” the Strawhats and to fulfill his duty to the Revolutionary Army.