What is the typical % that banks loan on Insurance Premium Finance Company receivables?

Historically banks have loaned 80 to 90% of receivables and usually as low as SOFR (Secured Overnight Financing Rate) + basis points. Start-up premium finance companies are usually prime + 1% until the bank can see the low mark off numbers in action.

Why such a high lending rate?

The very low mark off / bad debt reserve is the result of strict state laws governing the insurance premium finance industry as documented in this document and from the experience of those listed in the overview references.