Answer:
Because Pizza Hut is operating in a monopolistic competitive market.
Step-by-step explanation:
A monopolistic competitive market is one in which different sellers are selling variations of the same product which are not substitutes.
To stand out and survive , the sellers need to constantly differentiate or evolve their product by producing new styles
Back in 1958 when Pizza Hut opened its door for business, the product 'pizza' was relatively new and was in hot demand.
However as the years rolled by, many more businesses entered into the pizza-making industry causing stiff competition.
As the product remained unchanged, companies like Pizza Huts started making variations to the make up and composition of their pizza to set them apart from others. Hence they started evolving by making pizza styles like the Stuffed crust pizza, hand-tossed pizza etc. The new styles brought them profit in the short term.
2) However because a monopolistic competitive market is an open market with free entry and exist, other pizza making companies started innovating and producing similar new styles introducing competition again. The competition swallowed up the little profit margin hence over time the strategy of producing differentiated product and not an entirely new product is not profitable on the long run