I suspect the increasing proportion of online stores offering these deals is due to the increasing proportion of payment platforms (Stripe et al.) integrating w

I suspect the increasing proportion of online stores offering these deals is due to the increasing proportion of payment platforms (Stripe et al.) integrating with the buy-now-pay-later operators, and stores seeing no reason not to allow customers to pay using those methods. That said, a lot of these operators seem to be offering 0% interest: let's see how long that - and they - survive.