PvP builds both past (on live) and current gain traction because of a combination of popularity, convenience and specificity. Popularity in the form of flavor of the month builds that proliferate zones, arena and fight clubbing. It is a logical decision for someone to roll a character that other people have demonstrated has utility in action. Attaining that level of competency with the build may vary however, and this may have the unintended effect of slowing down innovation. The convenience of a build comes from a combination of viewing PvP builds before the character is created and knowing the outcome ahead of time - imagine leveling a character to 50, attaining and outfitting 500+ million in IOs, accolades, Incarnates, etc. only to realize that the build wasn't what you thought it was. A lot of people choose that convenience over the trial and error method. Lastly the specificity of a build plays a huge role in its utility - taking pool powers like leadership benefit team environments in zones and arena, but offer minimal solo player benefit when compared to IO set bonuses (I would say Tactics benefits solo players when slotted with +Perc) - you can't use vengeance without a teammate.
Now that the game is not as much of a time-sink (1-50 in 3 hours, Inf is easier to attain, incarnates easier to attain, etc.), as well as trying out new builds on the Beta server or private server ahead of time, and having a PvP community that is very supportive to new players goes a long way in making the game playable.
Lastly, I wanted to point out that I have fun when I play my melee character!