Everything can scale if you throw enough servers at it. Of-course Shopify scales, they even spent time and money to build a JIT on top of Ruby. As a smaller company, does everyone have the time and money to spend on servers or optimising the language to this extent?
That's the nice thing! You don't need to optimise the language and build a JIT as a smaller company, Shopify already did that for you. Just like Google did for Javascript, which lead to Javascript having any performance at all (which lead to node being a thing).
Also remember that Shopify didn't start out making billions. They started as a small side project on a far, far slower version of Ruby and Rails.
Same with GitHub, same with many others that are either still on Rails or started there.
You can optimise things later once you actually have customers, know the shape of your problem and where the actual pain points are/what needs to be scaled.
To me, I care a ton about performance (it's an area I work in), but there's not a lot of sense in sacrificing development agility for request speed on things that may not matter or be things people will pay for. Especially when you're small.
Smaller companies have less traffic, need less expensive servers, and have no need to spend money optimising the language. They can focus on that when they make billions of dollars, like Shopify does.
