Amazon's in the perfect position to give loans to their sellers. They have all the data in the world about how a seller is doing on the platform, so why not make some (relatively) safe money off interest and boosted sales?
Presumably it helps with inventory management too - like the loanee indicates the inventory they're buying which means Amazon can factor that in.
Then they charge interest ...
However, whilst this sounds good for Amazon, is it more efficient - in economic terms - or does it just reduce Amazon's risks and costs.
In the vast majority of cases money is released within 2 weeks of a sale. The exceptions are if an account gets suspended, or if there's a sudden increase in sales and it's flagged, in which case they might hold it for another week or two.
The only time money is held for over a month is if the account was suspended and not reinstated by then.