Your link doesn't work on mobile. Yes, I get that it's a dev site, but as Shopify is aware most users encounter most sites for the first time on their mobile device. I'm not the only person hitting this page on their phone wondering "I wonder what this looks like - is this interesting enough for me to remember for later?" With no demo page the answers that gets a yes are far lower than if there were a demo page.

I don't get this weird objection to just letting visitors see the end result.

I get that it's a dev tool. I still want to see an example end result before I invest time in learning the dev tool. I'm not alone in that. There's a reason why "Demo" links are common. They increase the odds people spend enough time with your product to get to the point of adopting it.