There is no rhyme or reason behind insurance.
I don't think that's true.
The prices are generally based on claims
experience.
I remember reading somewhere a few years ago that the most likely cars to get stolen were 14 years old.
This was suprising but it was because they had rubbish
security comapred with newer cars.
This price may be high simply because the claims experience on that bike was high for theft.
I agree it looks like an anomaly but that doesn't mean there's no reason behind it.
Often insurers price something high (like any business) if they don't want the business.
It doesn't look like that in this case but if (for example) a business doesn't want young males, then they won't refuse they will simply make the prices higher. Any business will do this so that if they get business they don't want then at least they are getting a premium.
In this case I reckon it's down to simple claims experience (they do have databases these days).