When someone is hungry and they go to an online food ordering portal they are spoiled for choice. They might like your food and order it 6 times out of 10 but when they see other types of food from your competitors maybe they'll be swayed to take their business elsewhere.
Your business (or your clients) can benefit greatly by having all the services that food ordering portal offers within an app that contains ONLY your (or your clients) service.
This feature is part of a broader strategy to eliminate competition and reduce the chance that customers go elsewhere.