What if the Maegi's/Woods Witches banded together?

[Cyvasse Khal]

So I was thinking of how just how much impact a couple of these almost innocuous and minor Maegi characters have had on two of the most powerful major characters in the story. Maegi Mirri essentially rips Dany's life apart while she was with the Dothraki and curses her so she can't have children. Maggy the Frog lays out a bleak future for Cersei while she was a kid, which has been coming true, and the thought of what is to come has been driving Cersei mad, probably the most powerful woman in Westeros driven mad by a Wood's Witches words like 30 years ago.

Why couldn't all these practicers of magic (however many there are out there) band together to create some kind of powerful force? Right now they seem to be scattered individually throughout the region. The Dothraki are afraid enough of just one at a time to want to kill them on sight. If there was a whole city of Maegi's (like an expanded version of Pyat's HotU) who can cast spells, curses, tell the future, create healing/death potions. Surely they could manipulate things to whatever their motivations would be, and be a powerful and feared force.

[Leif]

I don't think they care about domination/conquest or about being powerful and feared. Maegi and Woods Witches tend to be solitary or live in small communities and none of 'em seem like they're power hungry.

[Cyvasse Khal]

Perhaps as more of a way of survival then, rather than to gain any sort of power. The Maegi in Essos can be killed easily by Dothraki, while in Westeros they are almost exiled and vulnerable on their own. I think their biggest motivation would just be to keep their practices alive, so strength in numbers would make sense to ensure that I think.