From talking to lots of people back when I raced and from personal experience over the years I reckon there are pretty much two types of heads, a Shoei suited shaped head or a Arai suited shaped head.
The only helmet that ever really felt 100% comfortable on my noggin was a Arai. I tried all shorts of brands and more than one Shoei over the years. Why so many? If you crash and scrape the helmet you must throw them away if you race motorcycles and that gets expensive so you eventually just end up looking for what ever is the best helmet that is being sold on special at the time.

