You'd think, but 2.9% off the bottom line in the form of a large fee every month is something most companies will look to reduce or curtail after a few months or years. If your only processing a few grand a month, Stripe makes sense vs a traditional processor.

Once you hit $20 million in sales ($300-400k), the difference gets very noticeable vs. paying one internal IT and a couple security consultants to audit the work.

I don't disagree; its no different than AWS: once you get big enough, its time to roll your own or bring it in house. Until then, lots of money to be made selling shovels.

No one looks at their SMB customers and says "To hell with that market, they'll just leave once they're big enough!" The market for people building from scratch is enormous.

The thing is, you can't roll your own in house, but you can replace Stripe at a much lower cost with a different vendor. They all process cards after all!