Ted here from Shopify, thanks for reaching out to us!
This is a great question! Where Shopify Payments gateway is available, Stripe is not listed as a gateway that's supported. So as you are based in the United States, Shopify Payments is available in your location which is why you can not opt for Stripe. Shopify Payments is the premier gateway used on our platform and comes with great benefits such as:
Are there any features in particular that are offered with Stripe that's not possible with Shopify Payments?
If there is anything else I can help you with, please let me know, I'm happy to help!