Why does the Amulet of the Black Skull specify that you cannot use it to teleport to another plane of existence?

The Amulet of the Black Skull from Tomb of Annihilation says:

You can use an action to expend 1 of its charges to transport yourself and anything you are wearing or carrying to a location within 100 feet of you. The destination you choose doesn’t need to be in your line of sight, but it must be familiar to you (in other words, a place you have seen or visited), and it must be on the same plane of existence as you.

Why does the description specifically prohibit intraplanar travel when it already specified that the location must be within 100 feet of you?

Are there any situations when this is definitively not a redundancy?

I’ve never played Tomb of Annihilation, is there an adventure specific circumstance I’m not aware of that makes both restrictions necessary in the descriptions?