Yeah I know, although we haven't seen the proof of that (which probably tells its own story). While that's probably right, I still have a nagging, unprovable, feeling there's more to it.
Siebold's on record as saying his defence, particularly off the ball, needs improvement and someone here quoted some pretty bad tackle stats a few weeks ago. A back rower who isn't in the right place and / or isn't completing tackles shouldn't really be near the national squad irrespective of other attributes. That's just as fundamental as being able to deal with the set piece as a hooker.
Maybe he should just go back to his school position of 12 and be done with it.