Hi Eric,
Most counties with 60m now have the WRC15 defined band (5351.5 to 5366.5 kHz) but those countries who had 60m before the WRC conference often had (and still have) either spot channel frequencies or mini-bandlets as is the case with the US and the UK. They do not have the WRC15 60m band that the rest of us have. The frequencies used by activators in the US or the UK are channels that they have used for a long time and don’t look to use overlapping frequencies unless they expressly want to try to get continental Europe contacts. Considering just SSB, 5357 kHz is a common spot frequency between the US and all WRC15 countries. 5355 or 5363 kHz are overlapping frequencies between the UK and WRC15 countries.
Why do activators use 14.285MHz ? beacuse it’s the international QRP SSB centre of activity frequency. What you need to be asking is why is there an SV net on that frequency in conflict with IARU guidelines?
73 Ed.