Shopify aren't going to add this, because it will upset their paid app owners. Its quite sad really because it's a such simple and much needed feature. Kind of like why you can't easily add filters by your product variations and price natively without have to awkwardly adding tags to everything.
Shopify just want to keep their app partner happy, and at the same time make us pay extra cash every month for these so called "premium app" features.
I wouldn't mind if the apps weren't so expensive, but for something like adding a decent product filter on your collection page for an e-commerce site is on average £15 extra a month. What a rip off.