https://thenextweb.com/dd/2019/06/04/why-does-macos-catalina-use-zsh-instead-of-bash-licensing/

Yesterday, at its WWDC developer conference, Apple unveiled the latest version of the MacOS operating system. Codenamed Catalina, it’s a fairly significant update for the platform, not least because of the changes that have taken place under the hood. Take, for example, the default shell, which has been migrated from Bash to Zsh.

— Christina "I Am Sadly not at WWDC" Warren (@film_girl) June 4, 2019