Processing margins are thin and they have a valuation ($36B) to justify, so they have to grow product margins where they can ("going upmarket"). Market realities/constraints.

That only works if you have a number greater than zero to multiply your margin by, though. Stripe is already relatively expensive among the payment processing options we have available. In the early years, that premium was justified for us because Stripe was also much easier to set up than anyone else at the time. But that was nearly a decade ago. Today, there is far more competition from other payment processors, while the experience of using Stripe as a merchant is far worse. I'm assuming that they've simply decided to focus their business on the larger merchants who are obviously worth much more to them individually, but those merchants surely have negotiated rates below headline and won't be paying an extra 0.5% for this either, so it's a puzzling move.