I think I said this before, if not, I thought it.
Your chicks probably had a lot of stress in shipping
(got too cold, were in transport too long) and a lot of time they just do not recover.
try to order chicks when the weather is warmer.
Ideal, Abbendroths, Murray Mc Murray, Sunnyside and lots of others are good hatcheries.
I have said it before and I will say it again, the USPS is very detrimental for shipping chicks. (and hatching eggs).
Yah, I realized that. all the ones that actually got mailed died. After that happened I hopped in my car and picked up the rest... they are doing better, but just by a little