Non roosting chickens...

Here's my guess, based on my own crew.....
If the roost is too rounded, they have a hard time staying on, I discovered chickens are not like other birds, meaning they don't grip around stuff. They prefer to put their feet flat and sit on them, (especially good in the winter to keep the feet warm) so they are much happier with a 2 x 4, it gives them more room to land when they hop up.
Also, check how high up you have it. I placed mine to high in the beginning and they were just too lazy or to big to get up there.

 

Maybe yes, maybe no. My chickens roost on a 1.5" round pole and seem to like it fine.

How high are the roosts? How high are the nest boxes? Where's the window? All these things can determine where they roost. My girls (and guy) have two roosting poles, one at about three feet and one at four. They hop on the three foot one to get to the four foot one, but all fourteen squeeze onto the four foot high pole, mostly facing the window.

 

I agree. I read an article from K State a long time ago that chickens should have 2x4s with the edges rounded off a bit. They need the width to rest their weight on. Too small of a perch will cause foot problems later.

 

What type of chickens do you have? I've found that some just don't (or can't, rather) get up on roosts. Silkies especially have a hard time jumping or flying up to roosts.