No it's perfectly reasonable. That open source software forms some part of a commons is not really a thing in practice. Open source software is ran by maintainers, those maintainers own the projects, and they do with the software what they deem fit. And even if it were, VSCode is basically a rewrite of Atom that reuses a big chunk of the original codebase, they're the same sort of project serving the same sort of market, and the community is much better off with only one of them.
Instead of letting it slowly bleed out and randomly catching stragglers with outdated marketing materials lingering on the web, they give it a swift death. Atom can go into the history books as an open source project that defined the industry for a decade.