Why does cat urine crystalize?

It does?

This is caused by precipitation of the uric acid out of the urine. Most cat’s diets are high in purines, and uric acid is a product of purine metabolism. Uric acid is poorly soluble in water, and will readily crystallize out of solution when concentrations get high (as when the urine begins to dry).

Is the high purine amount the reason why cats are so prone to kidney problems?

The cat urine that I keep in my home rarely crystalizes, and when it does, it is usually because of pressurization as a result of soo much cat urine being stacked upon other cat urine. It is amazing stuff, not to mention, great compliment to my home decor.

It can be a contributing factor, but the root cause of chronic renal failure is more often an accumulation in the kidney of the artifacts of immune response. Every time the immune system is triggered by any cause (pathogens, allergens…), some of the resulting antibodies and the substances they bind are entrapped by the kidneys and eventually damage internal structures.