Sleepy Maiden

Can someone explain why sleepy maiden’s effect of " The targeted card cannot be destroyed by your opponent’s card effects." only work while it’s on the field. Like I’m not sure if it’s like that on YGO Omega. But that’s what it’s like on EDOPro and an explanation would be nice cause my bases on cards gaining effects is really Lyrilusc and Odd-Eyes Raging Dragon. I don’t often play decks that gain effects when something is done. And if it’s something like the wording which is why it’s treated as a continuous effect please tell me for the future.

Sleepy Maiden gains the continuous effect of protecting the targeted card. If she is negated, or is no longer face up on the field, that effect would to longer apply to give the target protection.