The downward trend starts too early for the Internet to be the main factor.
Plus the 1995 generation change was different from 1975 in important ways. In particular, when 1975 failed, JWs still had the "generation" teaching to ensure Armageddon was not far away. Now since 1995 they have nothing, at least nothing credible, to prove the end is near.
Look at the statistics of religious decline in general, in particular since the 1990s. JWs are not exception. Most churches are dealing, many much more significantly in decline than JWs.