The big players in this space aren't just trying to provide a tool that designers use to create artboards. The big thing is having a compelling story to bring in the other stakeholders, like Product Management and Engineering to participate in the digital product design and handoff. Yes, developers inspecting elements and their attributes is cool, but that's also barely scratching the surface.

Think about integrating a Design System, a developer framework (React, Vue,) creating simulations/prototyping directly with the artboards (like click this button and see it navigate to this other screen).

On top of all that there's cloud access and management for all these designs, and collaborative editing.

All I'm saying is that the big players aren't just trying to build a piece of boxed software. They're going for platforms and a connected suite of services. It's hard to have all that as open source.