Rahul can request but he cannot force Rakhi. It was an opportunity given to 3 people (Rahul, Rakhi and Aly) and Rakhi used that opportunity in her favour.
If Rahul expressed his feelings in a better way and allowed Rakhi to take her decision, Salman would have asked Rakhi why she didn't consider Rahul's request. But it is no issue because that's how this game is. As one person's loss is another person's gain.
He did request initially. He was even ready to let her shred if it was 2,3 even 5 lakhs. But when it was 14 lakhs itself in the first round and Rakhi was ready to shred even that, he had to try and convince her. Aly was the one shouting and threatening to radh the task. Rahul in fact told Aly to shut up and let him explain calmly.