Shirley, (I am saying this in a soft voice as I type so I am not confused at trollong) one reason would be to officially no longer be a JW. Affiliation with a church can impact employment.
What about running for public office and people find out you are a JW.
If you were a member if the KKK, you could just walk away. If it was found out you were a member and you tried to state that you haven't been to a meeting in 5 years who would believe that or perceive it as credible. Yet if you have a letter stating you renounced those beliefs it is a different story.
Some people just want to officially sever ties and not have to worry about elders and others stopping by to talk you into returning.
Others want the protection da letters provide in that they do not have to worry in the early stages 9f leaving of having elders drop by every 6 months. It is just a matter of officially leaving a corrupt and disgraceful organization