Yeah I think they decreased the chance of getting a Ninja Tool ever since they introduced the Moon/Sun Scroll update. Also if nothing shows up after you completed a TI that means you either already reached the daily rewarding attempts for that day (which is 5 by the way) or you already reached the weekly rewarding attempts (which is 20 +5 when you include the Friendship TIs).

Oh I see, well yeah like I said it's pretty rare overall that you get a ninja tool from TI. Just keep trying I'd say. Eventually you will get what you need even if it will take a while. I think you just get pretty unlucky. Good luck though ^^