I think you guys fail to understand the full scope of things. The reason for normal yield curves has to do with increasing uncertainty about inflation, economy, etc. as dates get farther out. 3 years vs 5 years really isn't much of a difference. Especially when you are only considering F/G borrowers paying ~30% apr (who cares if inflation goes from up half a percent).
The driving factor is credit loss, and here you have to switch perspectives from an investor to a borrower. If you are a borrower in the F/G grades you typically need the money more desperately and have far fewer alternatives. These borrowers are like travelers walking on the edge of a cliff. 60 month loans means smaller AND MORE MANAGEABLE payments for borrowers. It is like increasing the walkway for that traveler from 24 inches to the dropoff up to 36 inches to the dropoff. I have worked in unsecured consumer credit, and manageable payments is necessity on the lenders part. Yes there will still be people that have no intent on paying, but most people would like to pay. Though once they feel like they can't live and pay, they will stop paying: ACH Revoked, cease and desist, account issue (aka they closed their account or issued a stop payment). Maybe the lower interest rate is meant to encourage those risky borrowers to take the option that will be more manageable for them.
This concept is also what infuriates me about LC collection process, but that is too long of story.