Just speculating here - he’s made his pile and is enjoying spending it. While he was active, he was really prolific - a lot of very hard work.
I recall that his last novel, which was about Ryan’s son, came about because at the time he still owed his publisher one more book under the contract, but he was also in the middle of his divorce, and his soon-to-be ex wife was going to get 50% of everything that had sprung from the time they were living together..i.e..the Jack Ryan books..but a “new” novbel..featuring the president’s son...would be exempt from this..so, to spite his ex, and keep some cash..he cam out with the new hero..
http://roomfordebate.blogs.nytimes.com/2009/05/24/one-tweet-over-the-line/?em
One Tweet Over the Line
http://www.tampabay.com/features/media/article1004019.ece
Hey celebs: Twitter isn’t your personal PR rep, and could you quit the navel-gazing, too?