It's easy to see how, taking a cut off the top of a huge percentage of online purchases is an insanely nice place to be.
I've personally found myself preferring Stripe-based payments when there are multiple options (such as PayPal and Amazon pay) as well. Maybe I'm wrong on this, but I feel like dropping my credit card details into a Stripe window is more private than connecting to PayPal or Amazon accounts. It feels more like just swiping a credit card at a store.