Some people need to make sure a project is functional with multiple Xcode versions, and among them are library developers.
Apple accepts App Store submissions from the two last versions of Xcode (currently Xcode 13 and Xcode 12.5.1). It's nicer for the users of a library if that library supports both versions.
On top of that, as time goes by, libraries that support a known set of Xcode versions at the time of their latest release will be compiled with newer Xcode releases as well. Again it's nicer for the users if the lib builds fine. And it's nicer for the library maintainers if a new Xcode release does not create mandatory maintenance.
Finally, dropping support for an Xcode version is a breaking change, in the context of semantic versioning (let's not forget to be pragmatic, though).
What is true for Xcode is also true for OS versions and Swift versions: in the end, yes: there is a strong need for code that supports multiple OS versions, multiple Swift versions, and multiple Xcode versions.