People used to complain about never being around for these official gm/es tourneys, and so the staff adapted to create more tournies, and place these tournies meticulously so that as many people as possible can have the opportunity to take part. And so, as Blur has mentioned, they look for when I good number of people are on (Generally around 7-12pm GMT seems to be the most populated time for the majority of players- personal observation not statistics) so they can give as many people that want to take part, the opportunity.
From my experience, the only times I've felt inclined to leave a bet server for a tournament is when the betting server had been below par, as only then did the tournament become a worthwhile alternative.
What I would like to see however, is scheduled bet servers (whether it's by a set roster of applicants or taken up as another role of the event squad) in these peak times- that are just left with one or two people in charge of the server, all rake goes to decapprize, and people can just be left to bet under the wing of an official server.
That is my side suggestion^