1.5% back on the purchase via CC rewards beats earning 1% over 3 months (4% yield) in a HYSA every time, anyone using BNPL is using them suboptimally.

For a 3 month BNPL loan to be worth it, HYSA rates must be over 6%, and actually a bit more due to the time value of money; you get CC reward cash after the statement period but it takes 90 days (and up to ~120 days) to get three monthly interest payments.