Obito knew very well that, compared to a few years ago, Uchiha Chi's strength must have grown even further. Otherwise, facing Nagato, whose strength was even greater than his own, it would have been utterly impossible to secure victory so quickly. Moreover, according to White Zetsu, Uchiha Chi hadn't just barely won—he had held an absolute advantage.
Therefore, Obito was forced to reassess the current situation. He realized that if anything went wrong with Nagato, especially if the Rinnegan were lost, his Eye of the Moon Plan would likely be delayed indefinitely, which was something he could never allow. Thus, at this moment, Obito could not afford to let anything happen to Nagato; he had to save him.
Though Kakashi and the others tried their utmost to block his path, Obito, resolved to retreat, regarded them as nothing more than insignificant obstacles.
Chapter 410