7000 kHz seems to be popular all over the place. When the propagation to South America is strong I often note Spanish and Portuguese voices on 7000 LSB and 7000 USB at the same time, regardless of what CW traffic is on frequency. Of course, there's also the lets use 6999 kHz USB or 6998 kHz USB crowd that get at least some of their audio over the 7000.0 kHz "border" (if you want to call it that).
I know the Latin Americans are fond of easy-to-remember frequencies and radios probably default to 7000 kHz, 14000 kHz, 21000 kHz, etc, as you flip through the bands, making it that much more attractive.