Why macos doesn't offer something like this by default is beyond me.

Really, there are some really smart people at apple. You know some of them have customized their environment. You know apple has internal tools.

Why don't they get it and support customization of their os?

They're also not very supportive of "outside" tools. Say you want to use python on macos. Apple has only the most passing support for it. Same with bash or anything else that could put up a dialog box or whatever without having to compile/use xcode/other barrier to entry.

applescript doesn't count.

I know you can add software like macports or homebrew, but I mean first class support from apple.