My sympathies on the damage. Much of the trees still looks nice and green, so it isn't overall plant stress. Based on my experience looking at my sister's deer damaged arborvitae, the damage looks like it was caused by some type of critter eating the bottom couple of feet of greenery. Do you have rabbits? The higher bare spots might have been caused by deer.

IME arborvitae doesn't grow back well from damage that removes all of the green in an area. Would you consider planting other shrubs around the feet of these to hide the damage? Or removing them and replacing them with something else?

It could be something has eaten them. Does the foliage appear to have been chewed?

The other possibility is that someone used a weed killer in the fall. Do you have a lawn service or did someone use Round Up on the grass or weeds in the area?

Steve