Well, first of all, most of the baptisms being recorded are not new converts, they are the children of Witnesses. All you have to do is go to an assembly and watch the baptisms. In my area, the baptisms are between 80 and 90% children.
The number of children is also decreasing, for two reasons. First of all, Witnesses have always encouraged singleness and pioneering, rather than having children. When my wife and I we having children in the 80's, we were the subject of numerous comments regarding starting a family with the end so near.
Secondly, JW's have always been poor at retaining their children. Only about half of JW children end up staying as JW's. It takes a certain type of insanity to convert to the Witnesses. This insanity is not necessarily hereditary. So, if you start with a low birth rate, and then cull out half of them, you get a big decrease.
In addition, the society seems to be mining their baptisms from younger and younger groups of Witness children. It is much more common to see 10 and 11 year olds getting baptised than it was in the past. So, even these lackluster numbers are misleadingly overstated.
Add to all of this the aging demographic in most western nations and the internet, and you have a recipe for a JW recession.