Subway is a business. It has no doubt done studies and market evaluations regarding this change. It is doing it to MAKE. MORE. MONEY. I would venture to guess that a lot of muslims eat at Subway and they are tailoring their menu to market demands. Subway, and any other business, would NOT change their menu or business plan to accommodate muslims unless there was money in it.
In other words, they aren't chicken. They are smart. Utterly without moral compass, without long-term planning, without anything but MAKE MORE MONEY NOW. Because: That's Capitalism!