It's a bit trickier than it seems because a lot of Obsidian configuration and app functionality is vault-specific. E.g. what theme should be used? What plugins should be available? Does autocomplete for [[links]] or properties do anything? Etc.
If you have a window open, the file is opened to the workspace for that window. You can see this in action because the "Trust" dialog specifically says that you're trying to open untrusted files into a trusted workspace.