The person who buys full fare tickets but doesn’t pick their own travel provider (either because they ignore it, their corporate travel department buys the tickets) isn’t going to spend more money on an airline because the loyalty program is slanted to high revenue travelers.
Yet a program can influence both choice of travel provider and total amount of travel. A business traveler is less reluctant to travel if she’s being rewarded for it. They may not fight against travel when they aren’t just getting their expenses covered but they have something to cash in later. Without a rewarding scheme, business travelers become more reluctant to travel.