Google fails me in my search for why Garleans cannot use magic.

I had assumed it was genetic since it is passed on to their children, but it cannot be the physical body that is the limitation. Otherwise Elidibus would not have been able to use magic in Zenos' body.

So that makes it a matter of their soul. Which also opens up the concept that traits of a soul, such as the inability to use magic, can be passed on to children.

Is there anything in lore that goes over this more in depth?

There is also the possibility that Elidibus changed the body somehow via magic to undo the limitation before going into it. That could open up some interesting plotlines if someone is able to find the switch inside the Garleans to turn magic access back on.

Does anyone here think this will be explored more in coming game content/expansions or just a case of "They can't except when we want them to. Don't ask questions"?