They admitted in the Watchtower a few years ago that there has not been an increase in earthquakes. So why are they still going on about this?
Because it hasn't sunk in to the rank and file JWs yet. They still use it as part of the sign. Every time there is a major earthquake, chain emails make the circuit with fudged data about the "increase" in earthquakes. In addition to wanting the JWs to keep up with "new light" the Borg wants deniability; even though the JWs spout off about an increase in earthquakes, the WT says otherwise.
It is kind of like the overlapping generation thing. Expect a re-hash of the doctrine at this summer's district conventions. Why? Because too many rank and file JWs still think the generation means anyone alive in 1914.
It has to frustrate the GB to hear that so many JWs stick with the message they learned before getting baptized regardless of what new information comes out.