Every week I get at least one email from someone looking for pet insurance that covers pre-existing conditions. I tell them that no insurance company covers pre-existing conditions and explain it this way: if you got into a car accident and then tried to buy auto insurance the next day, would you expect the insurance company to pay for your accident? Of course not. Well, a pre-existing condition is basically an uninsured car accident.
The reason the insurers don’t cover pets with pre-existing conditions is simple: pet owners would simply wait until their pet got sick and then buy pet insurance. And this would put every pet insurance company out of business within a year.
So it makes perfect sense that insurance companies do not cover pre-existing conditions.
There are a couple of additional details worth noting: 1) you can still get pet insurance if your pet has a pre-existing condition – your pet will still be covered for everything unrelated to the existing illness/condition; and 2) some insurance companies consider a pre-existing conditioned cured after a period of time (and will reinstate coverage for that condition.)