First of all, a "fad" suggests something that was real popular for a short amount of time. It may never get there. Also, you probably ought to qualify the statement I put in italics. SSB has not replaced AM on HF. It has supplemented it, and a majority of "phone" operators use it. To check the history of how that transition took place, you would see a prolonged struggle for acceptance of SSB because of its shortcomings that have included bad intelligibility, increased vulnerability to interference at comparable power levels, and a degradation of how hardy the equipment needs to be to produce it. Add to that list the incompatibility of SSB with other modes and activities --and it brings us to today, because that's the same linchpin confronting "digital" communications wherever they emerge among bands that are shared among a wide range of users. As for the ARRL’s influence at promoting “digital,” as a category or by endorsing a standard protocol, don’t count on much. The club in Newington was spanked very hard in front of the FCC a few years ago when a former staffer came up with a segregation by bandwidth scheme that could have opened the HF bands to enormous mode conflict. Their proposal would have used the regulatory structure to pressure acceptance of nascent digital modes. Active, concerned licensees sent the scheme down in flames and it was withdrawn before the FCC acted on it.