I've seen quite a bit of Kendo now and I always wonder why they do anticipating attacks. I mean they start their sword off in a position where they must draw back, but how is this good? As the open could then potentially attack them with a readied attack from their stance, like a stance. I've also seen a lot of HEMA, in which they do not anticipate at all, or rarely at least.
The position you're referring to is the most common used starting position ("kamae") for kendokas.
It is absolutely not passive, as all attacks can be done from this position. Standing in the starting position, the whole body is prepared for lunging forward by a push of the left leg. It's not very visible, because of all the clothing and gear the participants are wearing. You might have seen them been standing like this for minutes, just shouting and doing small movements. This is one of the most intense situations for kendokas, as they're just waiting for the right moment to lunge into an attack.
As mentioned in the comments, the tip of the shinai is pointing at the opponents throat. Moving strait forward will make the shinai hit the throat, and the attacking kendoka will get a point, if the attack is correctly executed. As for other attacks, it's not necessary with large draw backs. Often (e.g. in competitions) a kendoka will stretch his arms keeping the shinai in the center (while moving towards the opponent), and within the split of a second do a small cut to a valid point area. Bigger cuts with obvious draw backs happens fast and are used in combination with body movements (barely visible and very visible) to execute a successful attack.