[2021] Spider Zombies and football player zombies

My suspicion, and it's only that, is that they couldn't get the spider's crawling animation to look good, and that's why they became jumpers instead of climbers. As you'll recall, when spiders 'climbed' up walls, they played their 'walk forward on all fours' animation. It looked completely terrible and unshippable.

It may also be that they didn't like how a lip at the top of a wall would defeat spiders. By jumping, spiders can now overcome a broader range of geometries. I didn't mind this aspect, though. I thought it was appropriate that there was a building strategy to thwart one specific type of zombie, that you'd have to juggle with other strategies in your base design if you wanted it to be effective.