Timing
While you're correct in the particulars, I still find it difficult to believe that, after three years, this victim's indignation coincidentally reached a peak during that short few weeks after the Florida primary and before the election, when it was impossible to change the ballots in that safe Republican district.
Unless it happened exactly that way, somebody's been sitting on these incriminating messages for a long time, somewhere between a couple of months and two years, waiting for the right moment.
Whatever the motivation for this, concern for Foley's victims was not one of them.