because the third party lender puts the merchant through the ringer as that is their only security, so the merchant then has exposure to a third party taking security over their receivables and this would I dare say opening up their books, so it's an interrogation of sorts to get approval as a merchant under the SPT model go enable upfront payment collection, not as simple as some of the other models out there.
The lender also charges the merchant for the privilege and the lender will take payment from the merchant own receivables if payment doesn't come from the borrower/ customer, so risk.