Maybe that's what it was. It doesn't necessarily need to be that going forward, as project putlooks anf goals change with time.
Also editing is quite a lot of more work to support than mere viewing. As all tools and actions need to behave correctly - not jusbt the renderer.
And something proprietary can hadly be a "industry standard". It can be "most common" or a "de facto standard". But all "industry standards" are by definition open as any industry worth its weight doesn't rely on or include a single point of failure anywhere within itself.