Perhaps just me, but I feel that the beliefs and history surrounding the magical arts have more to do with their mechanisms than anything else. Sure, a thaumaturge could draw aether from their surroundings like a conjurer, but then that would just be black magic. Which is forbidden to their Order. Forbidden, and ultimately forgotten, out of fear and misunderstanding than anything else.
Alternatively, a conjurer could pull only from themselves, but why would they when they have nature to pull from? The moogles taught conjury to mankind so that they could communicate with nature, it makes little sense to isolate themselves from it.
In short, they are two unique magical fields with very different origins, history, and fundamentals. Trying to determine why one does things one way and one another could have many variables and no one right answer.
Alternatively, a conjurer could pull only from themselves, but why would they when they have nature to pull from? The moogles taught conjury to mankind so that they could communicate with nature, it makes little sense to isolate themselves from it.
In short, they are two unique magical fields with very different origins, history, and fundamentals. Trying to determine why one does things one way and one another could have many variables and no one right answer.