Why don't JWs or the governing body use the word shun?
Because if they use that word, they would be admitting that they are in fact shunning you. By not using it they convince themselves that they are not doing anything wrong, and therefore in their mind they are earning paradise on Earth by shunning you.
One distinctive characteristic of cults and high-demand, controlling groups is the use of unique, made-up words and concepts. The only organization (that I and the researchers I know, know of) that uses the word "disfellowhip" is the WT and the JWs.
Other groups use different, exotic sounding terms, concepts and words that they make up, to make their followers believe (a) that they are the only ones who have some kind of unique truth or knowledge of something no one else knows, and (b) that they are not taking harmful actions by not calling their actions for what they actually are. Followers buy into that nonsense and convince themselves that they are not doing something bad.
Other words/concepts that I have heard other groups use are:
1. De-foo: In one of those groups that word means that you are cleansing yourself from abuse from your "family of origin" (F.O.O.), what they are doing is actually shunning their family or "de-fooing" themselves. That group convinces all members that you were abused by your parents simply because you have parents, period. Every person has been abused according to them and therefore need to get "de-fooed".
2. Out of righteousness: Another group uses this term to shun family members who don't follow everything and anything that their leadership says they should. They believe that they are the only ones in "the right path", and therefore anything and everything else is "out of righteousness" and should not be considered worthy of anything.
3. Liberal: Some groups (and people) use this term to identify anything and everything that they don't like hearing from other people, or anything that represent things that makes them uncomfortable, or don't agree with. They use that term to dismiss and, therefore, shun people and things that they don't/can't hear about.
In my files I have a collection of ridiculous made-up terms that religious, political and other groups that don't care about their people use to mask their harming, shunning and/or isolating people from their loved ones. I used them in a speech I gave on cults and other high-demand, controlling groups.
The JWs use disfellowship, which is their made up term for shunning.