If the goal is selling more cars and trucks, it needs a captive willing to do things a bank wouldn't.
For instance, a captive will offer interest-free loans or cut-rate leases on a model with low residual value, with the understanding that GM will pay it back.
A bank doesn't want to take that much risk, and a car company doesn't want to pay an independent bank that much money.
That's a good argument for GM making a real captive out of AmeriCredit. And ironically, it was suggested by the head of GM's current designated lender -- a bank.
Ally Financial CEO Michael Carpenter explained during a conference call this month that Ally isn't interested in taking captive-type risks.
Which kind of takes us full circle. Ally is the former GMAC, which helped kick off the discussion in the first place.