Those that were frozen pressed on. Those that weren't, pressed on. While their movements were slow and easy to dodge, it was their numbers that they intended to overwhelm Sora with.

Once he was close enough, the zombies reached out to grab him. They didn't make any move to dodge; they wouldn't make it in time anyway. So they just met him head-on. You had better be quick on your feet, Sora, because as soon as you're near them they're going to try and surround you as well.