You make a good point point but it was hard to understand the way you phrased it: I think you mean that listing a discount rate (or any kind of pricing) wouldn't make sense because it is customer specific (history/existing relationship) and will vary accordingly?
I mean to say that the approval isn't really instant, as Shopify has already examined your cash flow and made a specific determination to market the offer to you.
The claim that no docs are required is also specious, as, again, Shopify already knows your personal information and real-time cash flow.
I would assume that the pricing is customer specific, which would make it more difficult to publicly advertise a price.