That's not entirely accurate. That is a revenue source in some models, but it's emerging and the value of market data, while valuable, may not be the biggest source of revenue for a BNPL lender.
No, the biggest source of BNPL revenue is merchant fees, which start at 2% and go as high as 8%, much higher than credit cards which range from 1 to 3%. The stores like these because they have clearly demonstrated that they can boost sales, and will take the merchant fee hit if their sales go up by 15-20%, and almost always it's on higher priced items, so those sales increases result in a higher boost to revenue vs. say 15-20% increase on lower priced goods. Larger items often have a high markup over their COGS because they take longer to sell (you're factoring inventory and cost of capital to manufacture for longer cycle time of stock converting to sale), so if BNPL speeds up the sale on higher priced, high gross margin goods then the saved cost on cost of capital and inventory holding goes right to profit. The merchant fees also are justified by the fact that credit cards tend to be used for high volume, lower priced items; it's rare someone is going to buy $1,500 and up on their credit card for a single purchase, but those are the exact purchase targets of BNPL lenders.
I'm not saying that's a good thing, unfortunately it's a good thing for the store and the BNPL lender but it's still not so great for the consumer. But for the most part these lenders make money simply on the fact that they speed up and expand the exposure for higher priced, higher gross margin goods, shrinking the time to convert stock to a sale, pay the store up front for the amount minus the fee, and recognizing real returns quickly. All at the expense of adding up debt on to people who likely cannot afford the extra debt.