It's that, or walk.
Those people that pay that rate are paying it through no fault of their own. They fucked their credit up and now they're paying the price because no real lender will touch them w/a 10' pole. They're a HUGE credit risk and are the type of people that will stop paying their car note as soon as it breaks down. I don't have the stats in front of me, but the majority of "in house" financing ends up being repo'd. The other shitty part of it is that people that pay we'll just say the state max interest rate also pay way more than the cars worth...Often 200% more.
The way it works is the dealer gets like $1000 down (has 1000-1200) in the car and then will just plan on collecting the payments as they make them and when they stop they yank the car and sell it again. Wash rinse and repeat.
And since BHPH doesn't report to credit bureaus the customer will walk from the car and go to the next BHPH dealer and do it all over again.