Because there are loads. I mean, almost every major technology company on the planet.
Indeed, there are lists of the "biggest" YC companies and it's remarkable how stratified the core technologies are with the launch year. Around 2008-2011 and it was Ruby all over the place. A number of recent companies list Go as the foundation of their solution. Recently Rust has started to appear in the lists.
Shopify is successful because of a business model at the right time and right place. That they use Ruby should be ancillary, but the company seemed to have hired the "big fish in a small pond" from the Ruby world so now they're cargo culting hardcore with Ruby there, making Ruby their core technology identity, to the point that they're spending enormous engineering effort to gain the benefits that everyone else is enjoying for free with alternative platforms. Which...they can afford it. But it doesn't make it right.