For one thing Paddle is a merchant of record so it's more like "outsource your entire payment system including all the processing of different payment methods and the global tax admin". For a lot of businesses, particularly smaller ones with international sales, that is going to be an attractive option compared to services like Stripe even at this price point.

For another thing Stripe has introduced so many extras that bump up their cut now that some types of business will end up paying quite a bit more than the analogous headline rate. So even if it were an apples to apples comparison the difference on the bottom line still wouldn't be as wide as it might first appear for those merchants.