Do those companies still run their businesses on RoR? My impression was that companies started out with it, but migrated to something more robust as their traffic grew.
Shopify is actually quite active in Ruby development and famously uses the new JIT compiler.
Stripe is still in on Ruby too; they're behind the Sorbet gradual type system, and Ruby is a first-class language for working with their API.
I always hear the stereotype of companies starting on Rails and migrating later, and I think it sticks around because it makes some level of intuitive sense, but it doesn't actually appear to happen all that often. I guess successful companies don't see the need to rewrite a successful codebase when they can just put good engineers to work on optimising it instead.
[0] https://shopify.engineering/ruby-yjit-is-production-ready
Amazon was recently hiring for Rails to work on a podcast app they bought, too.
There are a few acquisition companies and teams using Rails inside Amazon.