Because that's how A star works :) It's a graph search. Imagine adding an out-of-plane edge that travels from behind the starting point to the goal. Since tami

Because that's how A star works :) It's a graph search. Imagine adding an out-of-plane edge that travels from behind the starting point to the goal. Since taming that path could be optimal it has to check - it doesn't attempt to reason that such a path would necessarily be obstructed by what's been explored thus far. It's just a graph search.