Due to numerous fansites, successful new Guild Wars builds quickly spread in use. Some new ideas become so ubiquitous that they come to dominate one aspect of PvP, with a large number of similar looking teams using the current Flavor of the Month build. This is helped if the build is easy to adopt and can be assembled by a small number of "character parts", thus making the search for team members easier.
Guild Wars has a Rock-Paper-Scissors like mechanic: If one build becomes more numerous, it also becomes more useful to run counters to this build. Therefore most Flavors of the Month die out once the counter becomes more common. However, there are instances when a new build is so successful that it resists simple counters. Since ArenaNet is very concerned about balance in PvP, this usually means such builds will get nerfed sooner or later. A very famous example of a Flavor of the Month build, which dominated Heroes' Ascent for several months is IWAY but there have been many other Flavor of the Month builds.