Then I guess you understand the main reason a major component about the outrage: they’re not just shipping more value to customers. They are effectively making themselves the next version of Nix.
While a lot of people would be frustrated or annoyed if they had made those changes in an explicit fork with a distinct identity, they did not.
Putting my FUD foraging equipment on, this is looking like the last E in the infamous set of three Es. They’ve embraced Nix. They’ve extended Nix already (with the value proposition). Now they are actively extinguishing the upstream Nix project by making fetch happen themselves Nix 3.0, the next version of Nix.
No amount of platitudes in the form of PR-like word salads excuses this overt attack against the self-determination of the Nix project.