Cuz the jutsu is too overpowered, and i don't want to hear some people say. Kakashi will kamui him and it's over.Old or prime, if Prime, then why on earth are you restricting Kamui.
Hiruzen is too overpowred by fanboys, but he takes this.
Using reaper death seal and he die also, forgotten? So he will never do that, unless he wants a draw
Kamui restricted? I'll say Hiruzen has too much in his locker for Kakashi, although this deos depend on what kind of condition Hiruzen is in.
When he uses reaper death seal, he already sacrifice his life shadow clone or not1 shadow clone + reaper death seal = No death.
When he uses reaper death seal, he already sacrifice his life shadow clone or not