The problem is the Gnome team doesn’t give a flying rat’s ass about maintaining a stable api. I’ve never bothered with extensions because even the most basic stuff only works for one or two versions. The neovim team is pretty committed to backwards compatibility and following standards for interoperability like LSP these days, so it’s much easier for third parties to maintain a large set of extended functionality at this point. If they acted like the gnome team, your status bar plugin would break every other update.
This is basically just a way nicer, more flexible cron syntax being dressed up as something ridiculous. There are legitimate reasons for wanting something like this, like running some sort of resource heavy disk optimization the first Friday evening of every month or something.