Geico actually does use agents. I know one. But, it's like anything. All companies have marketing budgets and the bigger the company, the bigger the budget (usually). And certainly the cost to run commercials is ultimately in the premium -- just like McDonald's commercials trickle down to your 1/4 Pounder. It can affect the bottom line as AFLAC isn't the most competitive company that sells the type of policies AFLAC sells. But, undoubtedly AFLAC is more of a household name than their competitors regardless of whether they're more competitive.
You'd have to look at their marketing budget and you'd have to look at the premiums they collected to determine the answer. OBVIOUSLY the money to run the commercials comes from the premium because commercials aren't free. Premiums are indeed regulated by the commissioners but the premium they approve contains the companies' cost to do business.