Before the recession pre 2006 there were many car finance companies as the banks were lending and there was little risk. There was more supply to meet the demand which was beneficial to the customer as they were able to obtain lower rates.
If we fast forward a little, before 2007 the recession came and hit the finance companies first with a knock out punch. The banks stopped lending and it was the end of the road for many companies. Lending rates were at a high and finance businesses that were hanging on in there were having to rethink their whole strategy as some lost everything and were starting from scratch after years of building their success.
Lending the companies own money meant that they did not have to rely on banks and were in control of the rates. As risky as it sounds at least if another recession hit it would not affect them as much.