I work in payments. I'd guess the 1% on top of 3rd party integrations is to encourage folks to go through Shop Pay, which is owned by Shopify.
As for why people don't self host, it's likely just easier not to. You start off on an easy platform because who knows if your business is gonna work, then the business grows and you're already on there so why self host when it's working right now? And you continue down that path until it doesn't anymore.
As for why people don't self host, it's likely just easier not to. You start off on an easy platform because who knows if your business is gonna work, then the business grows and you're already on there so why self host when it's working right now? And you continue down that path until it doesn't anymore.