Most of the pre-New Year's Day bowls are not just broadcast by ESPN. They are also owned by ESPN. And to them, the whole enterprise is more about TV inventory (and controlling the bowl system) than it is about filling seats.
But if you somehow expect Sun Belt, MAC, and Conference USA teams that struggle to put 25,000 or 30,000 fans (and sometime less) into their HOME stadiums to somewhat sell half or nearly half of the tickets to a game in a 65-70,000 seat faraway bowl destination, it simply isn't realistic. If those teams can get more than 5,000 fans to travel any major distance, they've probably done very well.
Shifting the major, BCS-legacy bowls back to New Year's Day should help attendance at those games. And if the bottom-tier bowls can focus more on travel distance and attracting close-by teams (like the New Orleans did this year), they'll do better as well.