They’re still A Thing for App Store apps I think, but:
- using App Store for Xcode was historically very painful and ~nobody who uses Xcode daily downloads it from MAS
- it never worked ~that well~ for Xcode anyway - apart from the big download sizes, the problem with Xcode and the bundled SDKs is that they’re all approximately trillion little text files, and it’s not unheard of to wait longer for codesign (technically unxip) verification than for the download itself, which negates the user-facing benefits of delta upgrades for many users.