Why is notify-send included in Silverblue, but not zenity?

There are two often-used commands for basic GUI messages (notifications) from CLI scripts: zenity and notify-send.

It may sound as a useless question, but for a project (that just needs to show some notifications) I am trying to find out the differences between these two.

So I noticed notify-send (provided by libnotify according to dnd) is installed, but zenityis not. Both are actually included by default on Fedora Workstation.
So why did it happen?
Can I infer from that that notify-send may be more popular/common across distros than zenity?

Most likely it’s just that something else wants libnotify which coincidentally includes notify-send.