Why is it a Subway (sub shop) rule that you cannot give your order in the form of a note to the employee making your sub?

I just got back from Subway (sandwich shop), where I picked up a couple of subs for my neighbor. He had typed out a short description on what he wanted on the subs. I started reading it to the Subway employee and then I just handed it to her, stating that it might be easier if she just read it. Shen then told me that she couldn’t take the note. I asked why and she said it was against regulations but she wouldn’t (couldn’t?) tell me why.

While she was making my order, I thought about this and concluded that maybe they can’t be having things passed back and forth over the tubs of open food toppings, so I asked her if that was why, and could she have taken the note if we were standing over the register (no food there). She still said no.

Please know that I was very courteous to her. I was just very curious as to why that would be a rule.
I mean, we pass money back and forth…

Any ideas?