Thank you for contacting Ask Extension. Looking at your arborvitae, I am not sure that you will be able to get any new growth on the bare areas.

It is also important to ensure that the plant is not over-pruned, as yours are, as arborvitae do not respond well to hard pruning, and they may not produce new growth if pruned too severely. When pruning, one must not remove all the foliage from any one branch. Since new buds are only produced on branches with new foliage, new growth will not emerge if one cuts off all the foliage on a branch, so it's important to avoid this.

Remember, arborvitae are sturdy plants with very few pest problems, but they do require proper care and conditions to thrive.

Let us know if you need any further information.

I have included a few publications for your reference:

Arborvitae stands tall as easy-care hedge | OSU Extension Service (oregonstate.edu)

Oriental Arborvitae, Thuja orientalis (also known as Platycladus orientalis) | VCE Publications | Virginia Tech (vt.edu)