One reason behind decline of JW in industrial world is demographic. Wealthy countries had aged and there is less possible chance for middle age person to join a religious organization. JWs had tremendous growth there in postwar era coinciding with babyboom that lasted till 1960's. Once this wave aged in, there is very low probability to recruit new members outside your family. Second issue is increasing communication and education reach, which makes the indoctrination too difficult. And lastly, industrial countries do not base their national and personal identity on religion anymore with an exception of Bible Belt and couple extremes. In 3rd world countries, religion makes a significant part of personal identity, even more than professional life. Countries in Africa are heaven for various extremists basing their crazy ideology on religion. This would not work anymore anywhere in 1st and 2nd world (newly industrialized countries), as majority people would reject such nonsense.
Similar trends are happening in countries which are middle income like Poland, Czech Republic, where religion is not playing anymore any role. 25 years ago, JW experienced significant growth, but this had leveled off and went to slow decline. As more countries wil get prosperous, JW and other crazy groups will experience decline. Even Mormons, 7DA did not experienced extensive growth as they had hoped 25 years ago and most of them had abandoned Eastern Europe all together. The biggest exporter of various crazy religion in past 200 years is USA where most of the new religions materialized in modern era. However, outside they cannot make much difference on the world stage except in deeply impoverished countries.