This is also why archers only get one attack per round if they run too far, no matter how long they wait within that round; the game will not bunch several attacks up at the end of the cycle if you cross over that distance limit, it will just make you wait until the beginning of the new round and skip all of the attacks you missed.
It's just how DnD combat is structured in the rulebook, particularly 3.5e as far as I know. You only get a certain amount of movement per round. It's kind of a shame, and it doesn't translate very well to an action game, since it encourages finding a good place and then standing in one spot and just blendering enemies. Not very interesting or authentic, but it is what it is.