By 2013, Burger King’s sales were falling. The company tried a different strategy, shifting toward fewer products that would each have a bigger impact. New products would be easier to create, so they could be made more quickly with fewer new ingredients. The result: Burger King’s sales rose in 2014, and in the first quarter of this year its same-store sales rose nearly 7%. The chain’s relationship with operators, based on interviews with franchisees, is as good as it has been in years.