Because he doesn't seem to be a "follow me" type leader. He is an exemplary professional, and he is tough, he has shown that many times. Really he would be ideal for a club that has plenty of other professionals where he can just do his job alongside them.
He is no Kevin Campion, actually come to think of it we haven't had a Campion type since, have we? Even Rueben Wiki went off the boil somewhat here and Steve Price was the model professional type who clicked off his KPI's and went home.
Sort of why I hope we target Josh Jackson. I could tolerate the terrible back row balance in our squad for another season if we're actually recruiting true leaders to help get us out of mediocrity.