I've yet to hear a good explanation from them. So let's try to put one together. Yadier Molina may have given the most revealing when he said the goal is to be "Aggressive" and to remain "aggressive." And that invites the question on whether the pitchers have the control to be aggressive. Reyes has a history of a high walk rate and the stuff to avoid it. Gant's walk rate is harder to understand, given that he could and should attack the zone and get the grounders that lead to quick innings.
If the Cardinals are being "aggressive" to confound the launch angle craze and they're unable to hit the spot for those pitches, execute those pitches, then walks are going to happen because those pitches are often going to be out of the zone. Dialing back in the zone has been an issue, as we've all watched.
One thing that the Cardinals are tracking internally is the non-competitive pitch. This is sometimes known as a "ball out of hand." It's a pitch that can be dismissed that early in the delivery. Hitters can just ignore it. There are a few Cardinals pitchers who have pitches that the hitter can just ignore. That slider isn't going to land for a strike -- so see it, ignore it, wait for the fastball, or take the walk. That kind of thing. If a hitter can dismiss one or two of the pitches, he has an advantage, and an increase in walks would happen, too.
Another revealing answer came from Adam Wainwright. He said that it can be a cascade effect within a pitching staff if not caught quickly. He said the walks start to mount, the next pitcher tries to be too perfect to get everything on the right track, the mounts continue, and all of sudden the group as a whole is trying to avoid walks. He said that's no way to pitch.