Because the majority of current Jehovah's Witnesses are not students of the Bible. They follow the direction of the Governing Body (the Faithful and Discreet Slave) by reading and studying the publications of the Watchtower Bible and Tract Society (the Organization).
The GB says to shun (no talking, no greetings, no meals, no visits, no phone calls, no letters, no emails, no text messages, etc) any member (or former member) who no longer abides by the 'rules' set forth in the Organizations publications.
If any active member ignores these 'rules' they will be shunned (by family, friends and any Witnesses in the congregation/circuit/district/country/world).
No compromising. Not a personal matter. Period.
ginger