Popularity is a good reason and correct, but I will try and dig a little bit deeper.
A lot of players, including myself, are turned off by FPS games because of the accepted and expected behavior of the various FPS communities. These communities are full of every age range from 55 on down to 5 looking to one-up everyone else and let you know about it when they do. As a consequence of this hyper competitiveness, common human decency of treating people the way you would like to be treated is tossed out at the door.
Camping, griefing, killing at resurrection, and on are common if not expected in FPS play. Doing this raises your score or kill/death ratio nowadays. Players are rewarded for playing in a manner that is anti-competitive.
This is why I do not play FPS games in a multi-player manner for any long period of time. The constant struggle of who has the biggest e-penis gets tired real quick and takes me back to the horrid days of junior high school where everyone had low self esteem and the only way to boost your low self esteem was to pick on and bully other students.
Not my cup of tea. MMORPGS like the World of Warcraft where PvP is a part of the game instead of being the main multi-player draw is more my style.
