If you're doing less than a hundred thousand a year in revenue, you will likely save in development costs what you would pay in fees (3% x $100,000 = $3,000 = ~week of development costs).
Depending on which Stripe features you make use of and would have to re-implement yourself it may even make Stripe more affordable up to a couple of hundred thousand in revenue.
That makes it very attractive for side projects or bootstrapped companies, and side projects and bootstrapped companies often grow in to larger things, and at that point, changing out the payment processing is low on the list of priorities.
