More options to adjust pricing with dealers.

Repayments provide steady cash flow when sales are lagging. A auto finance business can become a general finance business (see Ally née GMAC) which may experience different business cycles than the auto business.

Loan servicing provides a marketting channel and a legitimate interest in monitoring borrower credit (which could be used to tailor marketting).

Promoting purchasing vehicles on credit may encourage borrowers to consider a new purchase when the loan is paid off.