Here’s my recollection from my limited research on this a few years ago (in the US):
-High premiums
-Insurance company can cancel coverage or jack up premiums if your pet becomes expensive
-needing pre approval for coverage, so you may be dealing with an extra layer of beurocracy when you need to get your pet treated
-Notable risk of insurance company rejecting claims
-Maximumum coverage seemed rather low (ie they cap the amount insurance will pay per year or lifetime, so your coverage may dissolve if you end up having serious pet health issues.
-high copays, so you’re still paying a lot in the event of large vet expenses.
Basically, overall, it seemed like a scam in which, even for those that end up needing a large amount of vet care, you are likely to get less benefit from insurance than premiums.
All that said, I don’t think I did much research. I think I looked at a couple of pet insurance companies that seemed “legitimate”, looked at the details of their policies, did some math, and concluded “lol, fuck no!”