The search space for the plans is ridiculously large, so testing pre-conditions needs to be insanely fast. With AVX, you get to test up to 256 boolean preconditions in one go!

To give you an idea about search space: the Orcs have a repertoire of 115 possible actions. Stringing together a plan of let's say 12 actions (some plans are longer), gives 115 12 possible plans. That is a scary big number: 5350250105473711181640625

A* helps guiding the search through this space, but can only do so much. So every A* operation needs to be as fast as possible.