Actually, this is all part of my clever plan to encourage this particular climax. It's far more interesting than "Bad guys coming? Okay, *yawn* let's teleport away."
I noticed the same thing in Savage Tide. Adventure 11? Sail the River Styx through the layers of the Abyss. Awesome, huh? Except that PCs will get all uppity and be like, "let's just plane shift and teleport wherever we need to be." So much less cool.