I think the reason why some people officially leave the JW religion by means of committing fornication instead of officially disassociating is because of the following two reasons.
- (1) Apparently (based upon what I have online) is that JWs in general (including elders) consider being a fornicator (especially if one only commits one act of fornication) as being fare less bad than submitting a letter of dissociation (especially if the letter says one disagrees with a number of WT teachings). It has been reported on this site that the elders and the WT especially is worried that a JW (or recent ex-JW) may be what the WT labels as an apostate. it is said that is because they fear that the apostate might share their beliefs and knowledge with believing JWs and thereby cause them to have doubts and maybe even leave the religion.
- (2) I have read that if a person later decides they want to officially become a JW again (for example, perhaps in order to again have social contact with their JW family), they can more easily do so (and it might take less time to do) if they had been disfellowshipped for committing fornication, than if the means of them officially having left was by disassociation (especially if it involved what the WT considers to be apostacy).
- For example, at https://www.jehovahs-witness.com/topic/5719308305956864/who-partaking-upcoming-memorial-april-15-2022 bola said the following (the bold face is added by me for emphasis). "I am just partaking for the sake of it. I cannot be reinstated after I have disassociated for 5 years and not partake. I am actually aware of the FOG in Watchtower." I am not aware that the WT has that specific policy, but maybe it does. Is it mentioned in the book for elders?
People don't need to do something potentially very dangerous (and what many consider immoral and which will [or might] very adversely effect them for the rest of their lives) in order to quit. For example, they do not need to quit by means of committing fornication, theft, acts of violence, illicit drug use, etc.. Furthermore for most JWs who want to quit, it is probably best to not officially quit. In other words, probably the best way (for most people) to quit is not by getting disfellowshipped or by disassociating. Well then what other way is there to quit, other than doing so officially?
For most people the best way to quit would be to quit informally (instead of officially). How? It would be by simply becoming inactive in field service and by ceasing to attend all JW meetings (including the Memorial), whether one does so gradually (probably safer, if one wants to continue to have social contact with JW family members) or suddenly.