Because sometimes 9S humans like to live a little outside of necessity. It's called being alive and doing what one wants to do. If he wants to put a bowtie on a pod then let him put a bowtie on a damned pod. Not everything had to have a reason. He needs to teach this boy to indulge already.

"I was wondering what would happen if your boy stopped working. Thankfully you have plenty of them so you don't have to break your back doing your own work." He's teasing of course but if 9S doesn't pick up on that he won't care.

"Still, they are handy by the sounds of them."