To be fair, what a large portion of players
want is to do whatever they can to perform at their best. Some are monomaniacal about a job or jobs, and some are more interested in particular roles, which includes damage-dealing. In this sense, following whatever the trend happens to be at the time isn't a fallacy in reasoning, but the means to achieving what's more important to that particular player.
Albeit, a lot of people do this very, very poorly, as evidenced by the gigantic pile of garbage we usually find attached to the most desired classes of the time.