Quite simply, the spots were funny.
At the top of Cliff Freemans game in the early 90s, old people, monkeys, cheese pulls and crotch shots were currency, and Little Caesars was comedy gold. But it was smart advertising, too. Everyone knew the Pizza Pizza! line, the right voice to say it in and the fact that you could get two pies for the price of one delivered to your house. And while the mascot was a little cartoon man in a toga, the live-action spots may as well have been animated, such was the extent of any given gag. Training Camp was the first place where you could see military-like training drills for lovably dopey delivery men, and Focus Groupin which every possible demographic, including old people, tribe members and effeminate lumberjacks request more toppings on their pizzagave a dig to the industry as well.