Gil, Materia, and RMT bots

[Astrahime]

Can't you just vendor materia? The bots would just do that instead.

That's kinda irrelevant. Materia IIIs (which would be dropping from Wanderer's due to the IL) vendor for only 90 gil each, which would be a cut into their profits even if the droprate for them was 100%. But it's a lot lower than that, go run literally any SB/ShB/EW level cap dungeon and you'll see that it isn't 100%.