It is already here, Katherine, just because things are not talked about doesn't mean they don't exist. I am not saying one is better than the other. I am saying it seems like anyone who is looking for internal strength is coming from an Aikikai background...I could be wrong about that.
I have trained with both.
I believe that the stuff is "there" in the ki exercises but also believe that most folks never "get it" because it isn't explicitly taught ( at least in the Ki Society and offshoot dojos I"ve visited or trained in; admittedly my longer and/or more frequent experience is w/ Aikikai ) Many folks seem to think and train as if moving one's center is physically moving the entire pelvis/hip structure as a unit.
I will admit this is a case of YMMV, again, due to my experience being not that extensive.