Because it looks like line noise, is unreadable to anybody not a UNIX/Linux admin, and is a standard in the same sense that the directory separator is the backslash on the majority of deployed desktops and servers.

More importantly: It’s also not extensible without being completely changed, which makes it a poor design.

Fluent builders can be trivially expanded to support new capabilities without breaking existing code or configuration.

Cron’s syntax was likely a quick and nasty thing thrown together by some student at Berkeley or wherever in the stone ages of computing. We shouldn’t be bound by these accidents of history in the same way we shouldn’t keep using Roman numerals these days.

Maybe the better question to ponder is why is it something that needs explicit learning. It's a basic task scheduler.

The *nix format hell in general drives me insane. Immensely glad for the recent-ish trend of lots of applications at least slowly adopting JSON and others as both config and output options.