Why are oxalate rich foods bad for a patient with chronic kidney disease?

Oxalate crystals precipitate out of urine and crystals are harmful to the issues, including kidneys. Oxalates can also form stones. For more info: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3741982/#:~:text=Oxalate%20nephropathy%20has%20many%20etiologies,fibrosis%2C%20and%20progressive%20renal%20insufficiency.

Chronic Kidney disease means the kidney has problems getting rid of things which it is supposed to do. So moderation in diet is required which includes oxalate rich foods. For a proper diet regimen for Ch renal disease pl consult the treating MD