This is for consistency with
other effects that alter an entire class of things, mostly on Fear Cards and Event Cards. Powers that affect a single land, or a land and its neighbors (e.g.,
Bloodwrack Plague;
Prey On the Builders) – check state at the moment they resolve.
This is entirely for ease of play. For a single-land effect, it's much easier to check prerequisites at the moment of resolution and not have to remember, e.g., "oh, I need to leave a Beasts in this land to cancel the Build". For widespread effects, it's much easier to remember a general rule like "Invaders skip actions in lands with 2 or more Dahan" than it is to note and remember every single land with 2 or more Dahan at that moment, and keep that memory until the Ravage happens.
Tags: Defend, Changed rulings, Encompassing Ward, Bargains of Power and Protection, 2 more...