Are you sure that you're not confusing Prize Bonds with Government Bonds? I doubt that institutional investors are hoovering up Prize Bonds. They're not that dumb.
It was in the context of PB's that it was posited but then that was back maybe 15-20 years ago when the prize fund might have been about 3.5% of overall holdings so certainly more attractive to institutional investors. Anyway just recalling and repeating what I read back in the day, to discern whether there might be any validity to it (and also note DoM's follow up)