I see you missed him back in January when he was the monthly just like in the other servers. That's one of the reason why he is in 3v3 battles as he was given to people for free.

As for a reason why Anbu itachi not showing as often in events is due to new ninjas get priority and ninjas that people have asked a lot to be in events will be up as well (jonin minato, shisui). Itachi can come up in the future but don't expect him to be routinely like agk konan, 6p naruto, etc. come in events. So save enough coupons until you have enough so when he comes up again, you can spend up to the full 80 frags.