>>58555844As we've already mentioned, this is a reference to Regice, Registeel, and Regirock, which were once necessary to awaken it.
Here, it's not "the plates" that are needed, but the Steel, Ice, and Rock type plates, and NOT the others. And unlike all the other times, where Regice was used to trigger a reaction from Regigigas, here the plates are used to open a door.
This context isn't arbitrary. The need for these three types of plates also contributes to the game's linear progression, allowing you to advance step by step.
