Who does not like a free lunch at work? Especially for workers that do not bring their lunch. Small signs of allreciation do matter to employees. But, few landlords or mortgage lenders accept pepperoni pizza as payment.
The fact that free lunches keep people in the office and around their desks probably helps productivity the most. At the end of the day, not sure many people will truly stay at or join a company for the pizza if the compensation does not align with their needs.