Throw a puck to a goaltender, and they'll usually reach out and catch it, bringing their catch-hand closer to the puck. Shoot that same puck at the goalie, and many of them will try to "intercept" the puck, moving their glove vertically, but not towards the puck. Goaltenders that play this way will undoubtedly make several "spectacular" glove saves, but will allow many more goals overall.
One of the rules of goaltending is that, the bigger you are, the more likely you are to stop something. Well, that holds true here as well. The goaltender that "attacks" the puck with their glove is more likely to block the puck away from the net.
Also working here is another rule of goaltending: follow the puck all the way into your equipment. If your gloves are in front of you, where you can see them, it's a lot easier to follow the puck into them. With your gloves at your side, you'll find that - too frequently - you're craning your neck, shoulders and torso to follow a puck. When that happens, you'll not only stop fewer shots, but you'll be out of position for any rebounds that result.