Style matters to some people and of course there are also the ones who 'have to have' the latest and greatest. Economy of scale also makes a difference. Three sizes for the expensive one means different molds and seperate stocking at the stores. I would bet they move 5-10 times as many of the cheap ones.

Is the difference worth it? To me no. UNLESS it comes down to a fit issue. If you have a loose fitting helmet it can be a distraction (thus an actual danger) and also is less effective. SOME of the very expensive helmets are very much fit issues. They fit those who can not get a decent fit from the 'standard cheap' helmets.

Sometimes the most recent latest and greatest does have better impact absorbing properties. But unless you are into rather radical riding and actually expect to crash the difference on that level is probably not worth the price difference. (And you would need to do some research to find out which really are better on that count, it will not ba all the expensive ones).