Unreported sub or illegal sub

[Crabby_Bob]

Originally Posted by IRISHMAFIA

Speaking ASA, [snip] If the violation is deemed that of an illegal player, this must be protested by the offended team. (ASA 4.6.E)

Per the book, why is an unreported substitute (4.6.B) or an illegal player (4.6.E) handled as a protest rather than an appeal? A protest may mean stopping the game and finding the UIC.