How to update shell programs
The content of /usr/bin and friends is updated with each release of macOS, but usually the versions shipped by Apple are significantly older than what's available on Linux. There are various reasons for this, in a lot of cases it's related to changes in the GPL. In case of crontab it may also play a role that the use of cron is deprecated, launchd should be used instead.

If you want to update Unix binaries yourself


Use Homebrew (https://brew.sh)
Compile from source yourself and install in /usr/local/bin