One reason to keep in mind is backwards compatibility and the expectancy that every Linux system has the same basic tools that work the same.
Imagine you have a script running on your server that uses a command with or without specific arguments. If the command (say tar) changes its default parameters this could lead to a lot of nasty side effects from crashes to lost or mangled data. Besides the headache of debugging that, even if you knew about the change beforehand it's still a lot effort to track down every piece of code that makes use of that command and rewrite it.
That's why programs and interfaces usually add new options over time but are mostly hesitant to remove old ones. And if they do they'll usually warn the others beforehand that a feature will deprecate while allowing for a transitional period.
One way to solve this conundrum is to simply introduce new commands that offer new features and a more streamlined approach that can replace the older ones in time. Yet a distribution can still ship the older ones alongside the newer ones just in case they are needed.
Looking at pagers (programs that break up long streams of text into multiple pages that you can read one at a time) as a simple example you'll find that more is an older pager program while the newer less offers an even better experience ("less is more", ¿get the joke?). Both come pre-installed as core tools on many distributions. Finally an even more modern alternative is most, another pager with even better functionality, but you'll need to install that one yourself.
Didn't even know that this existed. Will have to try. Thumbs up for using mark up which makes it easy to export/import notes.