Don't forget Oasis isn't the one creating the ninjas, it's the Tencent - the one who owns the China server (the original server). The longer they do not add anymore canon characters, the longer they can milk whales. This is why you most likely haven't ninjas like night guy, kagura, or updates to the major story line.

They will keep on adding random characters like swimwear, suit, kimono, et*il they are getting tired of milking players.

Why would you think I know?

If you paid attention to what ninjas that show up, they are ninjas that aren't in the meta. For example, you won't be seeing edo minato, kakuzu, kushina red, or edo itachi to be given for free any time soon. Just look at the current list of nijnas in the game and you can figure out which ninjas might show up. It's not hard