Q & A: "Post-audition sequence with Saito in helicopter"
Q3.1) Why was Nash taken away by Saito’s bodyguards from the helicopter?
Answer: There are two reasons, with the latter being more plausible. One, Saito was not happy with Nash’s attitude and performance, and intended to give him in to Cobalt Engineering. Two, knowing that Cobalt Engineering would hunt for Cobb and his team after the botched extraction mission, Saito wanted to buy some time for them to rebuild a new team for the inception mission he would later propose to Cobb. Since, Nash was deemed to be more dispensable to Cobb than Arthur, Saito decided to give Nash in.
Q3.2) Why did Saito propose inception to Cobb?
Answer: Saito knew that Cobb had a reputation of being a skilled dream thief. Moreover, from the audition, Saito would have seen for himself Cobb’s strengths (but also some of his weaknesses). The fact that Cobb had committed inception before was also not lost on Saito.
Q3.3) Why did Cobb accept the inception mission?
Answer: It was the only way back to his kids. Saito promised to wipe clean all of Cobb’s criminal charges with a phone call after the success of the mission, which would allow him to clear the US customs as a free man, reuniting him with his kids.