Why don’t more mods allow hydras?

[Aristeia]

I think just from the standpoint of fairness it stands to reason that hydras can allow an unfair advantage to the players using them. For example in chess, go, poker, it would not be seen as "fair" nor common for two player to occupy one slot and play against another player. Mafia similarly is also a battle of minds and it would be unfair for certain slots to have more then one mind occupying it in many circumstances.