The ground looks very dry. Not even any weed growth. How have you been watering these? How deep were they planted and were they in a container or balled and burlapped? I also see signs of black plastic poking up here and there.....that could also be causing an issue.

I am guessing the pdx in or screen name means you are in the Portland OR area but clarifying location can also be helpful.

I have watered with a hose these depicted arborvitaes in general not often but occoasionally. If i were to zoom out, there is probably 75 feet worth of arborvitaes (mostly unwatered) but it's just these in this area that are not doing well. The larger tree trunks you see are trees that block a lot of sun as well.

They were in a container and balled. There is some plastic in the ground but it's very very old. and yes i am in Portland, OR

It is a combination of competition with the existing tree roots for water and nutrients, not enough water to get the new arbs established and likely a bit too much shade and too deeply planted. The plastic is not helping either and should be removed.

I dont know where you're located but my rule of thumb is every 80degree day my trees get a 20min soaking with the hose. Just like all living things when it's hot out we need more hydration. Your planting area is so dry it's like a desert.