I recently read an excellent article by JD Power and Associates that outlined 3 factors as to why dealers sent the majority of their paper to one particular source...they identified the following factors as the defining reasons.

1. Being able to interact with 1 underwriter
2. short application approval times
3. expedient funding

Read the entire article at http://www.fi-magazine.com/t_inside.cfm?action=news_pick&storyID=34463