Well i guess it might have something to do with whether there is a serious and widespread issue of airgun owners acting dangerously, or a small number of high profile incidents, as per most things. I don’t have the figures to hand, but i am pretty sure BASC will have some background on this proportion of incidents vs. number of owners?
Regarding the advances in technology, fair enough on multi-shot rifles, this might be worth more thought from the industry/ authorities (although of course, one shot at a inappropriate target is too many). As for power increases, well this is a set limit. It doesn’t matter how future-tech your airgun is, if you go over the power threshold (12 foot pounds for rifles, 6 for pistols) you require a firearms certificate.
So that would apply to airguns from the 1950’s and today. I don’t think pellets have come on a massive amount over that time (still a small lump of lead basically) either.
I think maybe compulsory membership of a club or BASC, which includes legal advice and insurance, might be the next step and could be a requirement before sale. This is basically un-vetted licensing and wouldnt require a massive increase in the cost of regulating firearms certificates for much more dangerous shotguns, rifles etc.