For an SMB, the 1.5% difference in costs could very reasonably be worth it over the extra time spent integrating with a different company.
I work for an online retailer and with Stripe we spend almost no time working on our payments infrastructure because Stripe handles so much of it. That's worth quite a lot to us! Also bear in mind that the 1.5% difference might be on the sticker price, but Stripe fees are negotiable and closer to industry norms at scale.
Which is admittedly crazy, but there's a lot of people out there making purchasing and implementation decisions that don't really care about the bottom line.