I like the chuckle bit Tiki...
After six weeks of not attending meetings, what I said to the sole elder who came round to find out whether I had turned rabid apostate or not was, "It's just not for me".
In truth of course I had become a rabid apostate and was full of loathing for the Watchtower and anything associated with it and I was so glad to have no further truck with the slimy organisation.
It was then announced at the KH that I was no longer one of Jehovah's Witnesses which in retrospect was like a denunciation of my character to my children; that I was now on the devil's side. Also I have no doubt that the announcement served as vindication of my wife's triumph as a brain dead believer and martyr to the cause; which would gain her a lot of sympathy from the faithful. (insert vomit icon)
So WIT, I think that "my heart is not in it" is an honest and rational response and it does not play along with the JW game of blind, unthinking obedience. You are not obliged to elaborate on your reason to the elders.
Eventually it could also start a message which when repeated, will reach the GB and inform them that their religion is useless garbage.
It is very much to the point that millions of JW's hearts are not in their religion.