This usually happens when an insurer refuses to pay the full charges. DaVita can't let insurers dictate prices so they will draw a hard line unless an insurer has enough of their beneficiaries dialyzing to have the leverage to demand concessions.
What did you hear? I'd guess it is a small insurer, with few patients, getting exorbitant per treatment charges in an area with little or no competition.
The "full charges" are off-scale, and insurance companies generally pay some sort of negotiated rate. I know my FMC clinic charges over $3K (list) for a single HD treatment; collected $445 from my private insurer and would accept about $245 if I were on medicare. I recently had an out of town treatment at DaVita and they took my insurance.
My doc (medical director of a Fresenius clinic) told me a patient of his was recently traveling and that a Fresenius clinic refused him because his insurance paid too little ... so the Fresenius staff found a DaVita clinic that would treat him.