Say the chain was bought out by a non-islamic group. They hated pork too for whatever reasons, and removed all pork from the menu. As the owners, they have the right to do that. In a free market if the customers disapprove of the new menu, they go elsewhere and the new owners would financially suffer for their decision. Additionally, competitors could leverage their pork-power menu and possibly financially gain from it.
Let them remove pork if they want to. They'll likely see a negative impact on business, and other business owners just have an opportunity laid on their lap.
That may work in the free market, but as the article states, there are public schools that now no longer serve pork or pork products.