isn't it all down to claims statistics?
Comparing the I30N vs a 1.0 Civic.
The I30N is still a pretty new car, so there's less on the road and newer (arguably we all look after a 1 year old car way more than a 10 year old one). It's also not cheap (sub 5k) 2nd hand, so out of the hands of some/most youngsters and early drivers. It's also a new model with no historic claims data. All means it's statistically less risky than a 1.0 Civic that that could well be a likely 1st car for a lot of kids, and have thousands of insurance claims going back many years. (Could you still argue that Hyundai is a less "desirable" brand than Honda too? less likely to get stolen/keyed/etc? many moons ago I had a Hyundai Coupe and I think that was often overlooked due to the "wrong" H badge)
As the I30N ages and drops in value, the insurance will likely increase as it trickles into the hands of younger kids and those possibly less precious about their cars (so the claims will increase, making the computer suggest it's "less safe").
I noticed the same when I moved from my MX5 to M135i - insurance dropped despite the BMW being brand new and twice the power. Insurance company explained that at the time there weren't that many M135i's on the road and loads of MX5s, so less claims and thus "statistically" cheaper. I guess the same also applied for my 6MPS as the insurance was abnormally cheap compared with similar cars at the time - not many about so not many involved in claims. (obviously this argument/observation falls flat with luxury low volume supercars, but I'm sure they're a different kettle of fish to mass produced Hyundais)