That is certainly a fair question and one I will answer only from my perspective and limited knowledge and experience. I admit I have never worn one of what I will call the European style FF helmets. Locally, we jokingly refer to it as a Fighter Pilot Helmet.

Defense firefighting tactics generally refer to fighting the fire from outside the structure, where large hose sizes can be utilized. Frequently used to protect surrounding structures or in large structures where there is major fire involvement. Locally the use of deck or deluge guns/nozzles are commonly employed in barn fires, they are generally loaded with hay and burn quickly and very hot. Preventing spread to adjacent structures is of major concern as the barn itself is often too far-gone to save. What is the significance for the style of helmet that can be worn while fighting an exterior fire? Water is generally not pouring down on your head and hence not down the back of your coat. Also, the chances of structural elements falling on you are minimal, so protection of the neck is not as critical.

Offensive firefighting tactics require an interior attack to isolate and extinguish the fire from other parts of the structure. Search and rescue of potential victims requires an interior attack. Frequently water from above floors or roof will flood through the ceiling, which will run down into your coat unless diverted by the large flange protruding from the rear of the helmet. This same flange also provides protection to the neck from falling debris.

And as already stated - tradition. The Fire Service in the US has incredible traditions, and like in many other arenas, some good some bad. It is just the way it is, change takes time.

I am sure other FFs can add their experiences and opinions, but I hope this answers some of your questions.

Pete