Think about it he died and disappeared in other words probably into hiding but what i think shodaime did to defeat him was remove his eye and thats why he probily wears that mask because you see itachi meat him and he still has the mask on either that or Narutos dad did it to defeat him at the appearance of the nine tails . and it also explains why hes a shell of his former self hes only at half the power
well thats my theory i fell what happened to his eye