if you have reasons to believe that you can grow faster than "the baseline", it makes sense to use that evidence to borrow from a traditional bank. If you are undertaking a risky business move, the bank will not want to lend you the loan, and this model stripe has is going to be the next best thing.
Having a stripe loan would make me, as a successful business owner, make that move much sooner.
All that gives pretty good dataset for building predictive models that tell how the business will do. These models could be actually better at predicting the future than individual business owner (on large population). Stripe has information about the past performance of many similar businesses while the owner just knows about his.
Also need to remember that business owner is not just optimizing for low APR. He should be still making money through the sales. So hopefully in total there’s still the financial incentive to have as good sales as possible.
In short, you’re charging the highest interest rate to those whose businesses do better than you expected and the lowest rate to business who underperform your projections.
As such, you’ve created a financial incentive to underperform, and are entering this business of lending money by literally penalizing the least risky borrowers and rewarding the riskiest borrowers.
When you incentivize something you get more of it.
Your borrowers know their business better than you, and you’ve provided them with a mechanism to exploit that asymmetry in information.
You sort of have to assume that your incentives will be effective: the customers who have the most reason to believe they are growing faster than baseline will avoid your product and those who are pessimistic will embrace it, greatly increasing your default rate.