Because Snell standards have always seemed excessive and for unrealistic extreme cases thereby compromising effectiveness in more common real world scenarios. They may have improved or modified the standards over the decades but to me the ECE standards seem to suit my needs better. I've unintentionally tested several ECE approved helmets at the track and as far as I know haven't suffered any brain damage so in a sense "stick with what you know" applies.
there is a whole market of novelty helmets out there that are probably closer to not wearing a helmet at all versus wearing one that has been certified in crash testing.
Not that I'm an advocate of wearing the cheapest thing on the market in order to adhere to helmet laws but at the very least any hard bowl-shaped receptacle worn on the head just may be enough to contain most brain matter after an accident to help out the road-side cleaning crew with cleanup. And there really is a need to thin out the herd.