Nobody is calling it a sport, it's called an eSport. You know, to differentiate it from traditional sports. Totalbiscuit made a pretty good video about it the other day(apart from the beginning where he suggests that the ESPN dumbass should shoot himself like he said he would)
OT: I watch a lot of different eSports. Mostly LoL, but sometimes I watch SC2/CS:GO/Dota2/Hearthstone as well. I just prefer it to watching traditional sports because it's something I like doing as well(so I have some understanding for the games and how much skill goes into the stuff they do), just like I know lots of people who watch traditional sports do so because they play(ed) that sport themselves.