Alvron

Mostly it comes down to the mechanics. For instance if you have a game that uses Spanreeds then it wouldn't make sense to have group PMs due to Spanreeds only being one on one in world. There could also be a PM spying role, which is fairly rare, so a group PM would be quite the pain to have in game. Other times GMs don't want a large group forming and sharing information so easily. In past the community has disapproved of trust groups forming as it can marginalize those playing but not in the group by not giving them an equal or fair say. If one person asks you to do something you can always say no but it a group of trusted villagers ask you to do something and you don't want to, it can lead to issues. I wouldn't be surprised if the anti-trust group mentality has seeped into the GMs thinking when making a game and they subconsciously went away from group PMs. There is no reason for your game not to have group PMs. No one is going to complain that they can talk to others.

Shì de, wǒ yíngle

Or so you think but really, I win.

Real question is why don't you have catnip on you.