This is completely different. Stripe/Braintree are ways to charge customers on their credit/debit card on your website, completely unwieldy for paying freelancers. You'd have to have freelancers set up Stripe merchant accounts and receive card payments, that would be very weird and broken use case, especially considering Stripe's fees. I can send a freelancer an ACH transfer for $0, why would I want to pay 3+%?

As for PayPal, some freelancer (especially outside US) do get paid using it, but paypal's fees are outrageous and we try to get anyone we can on an alternative like zelle, ach etc.