There are also mods which give more accurate understanding of lead times such as Nomogram's Dynamic Reticle. While these can be very helpful in terms of concepting out your shot, there are many players which lead shells without use of this specific assistance. In short, they can be a tool but are not required for play of the game.
Players have made mods that change shells into soaring Anime Girls. Mod-making is a diverse scene which involves people creating things that they would personally like to see whether or not they have gameplay impact.
From our side, we do evaluate mods and determine whether we feel them to be too powerful in terms of player-benefit. The mods in our Modstation have been ok'd by us.
There is a combination of factors in this case.
While the mod you are concerned about is seen by some as giving a gameplay advantage, we haven't found it to be required/mandatory for good play. It's useful for those that find it useful.
As the mod exists for those that would like to use it, taking the time to recreate it in game isn't needed for it to be available for players.