A few friends have got back on bikes after bans and still found the premiums lower than their car insurance....why?....call me cynical but in virtually every car RTC i've been to the parties involved are practically salivating at the prospect of compensation, the collision may be minor but you can bet your mortgage on everybody involved complaining of neck pain and wanting to be seen in hospital....and looking forward to the cheque in the post.
The majority of vehicle accidents will involve damage to property rather than people, so its the third party costs of walls, houses, crash barriers, lampposts and repair costs of other vehicles etc that insurers will most commonly meet the cost of rather than death and injury, and obviously a car can do a lot more damage to things than a bike. Even though killing and injuring others is very costly its rare in relation to damage to 'stuff'. The kind of compensation culture whiplash claims you're referring too are deliberately low value claims, lower than most repair bills, as they're deliberately pitched at less than the cost, time and bother of challenging them.
However car drivers potentially have 4 other humans in their vehicle, all of whom are third party responsibilities of the driver so thats also an issue in accidents that don't involve other road users.
Also - most M/C riders are a bit fair weather, it'll rarely be their main form of transport, so even though the risk per mile of riding bikes is very high (200 miles on a bike has the same micro-mort score as a day on the frontline in afgansistan) the time exposed to risk is very low compared to car driving.