macOS ships with some GPL2 software, along with its BSD/MIT/Apache-licensed Darwin layer. (The GP is presumably implying that having this GPL2ed software "built-in", helped macOS entrench itself as a useful POSIX for developers — at least before tools like MacPorts/Homebrew came along to make acquiring this type of software "after-market" simple.)

For any GPL2 software macOS makes use of that then transitions to GPL3 licensing, Apple can't actually adopt the GPL3ed version (exactly because of the "runs anywhere" clause in the GPL3) and so instead, macOS keeps the old, GPL2ed version of the software around, left to rot. Eventually, if it's something critical, Apple removes their dependency on said software, replacing it with something that's not GPLed.

This is the story of Bash on macOS: it was regularly updated for as long as it was GPL2-licensed; then it got "stuck" on the last GPL2 version when GNU transitioned Bash to GPL3 licensing. The Bash on macOS remained on that old version for the longest time, before finally being swapped out for Zsh in Catalina.