because they think it looks cool and it looks very stupid. Also mostly gamertags with "iTz" in there turn out to be crappy generals or boosters. Well all the ones i met anyway.
true dat, i actually have a video of one cheating in matchmaking. it looks like lag but noone else was lagging. this guy spawned a banshee halfway accross the map and killed me with it.
The only iTz i have ever heard of is this guy called "iTz NeXn". i played with him somewhere and his name stuck. i remember it really well for some reason.. i dont know why though. what i do know is that he was popular or something.. maybe they all based off of one person? like i remember back when i played runescape, people all put I's in front and behind their names because there was an amazing PK'er named I Mohatma I
I think that there was a clan in Halo 2 named iTz, which stood for 'in the zone', then everyone copied it. Don't quote me on that though.