Why the switch from Montefortino to Coolus/Iperial helmets happened?

[Robert Vermaat]

I have a theory (as I've probably mentioned before) that the riveted composite 'Intercisa' and 'Berkasova' style helmets were possibly stronger than the earlier one-piece-bowl types, and probably much easier to repair. The rivets would absorb the shock of impact, and a single broken section could easily be replaced, rather than having to discard the whole helmet. I confess that's just supposition on my part though!

Some people seem to think the new style ridge helmets are of (far) lower quality! (But they they may just be infavour of their Principate helmets..) I guess it has not been tested so far. Rivets could indeed absorb impact, but when weakened, the whole construction comes apart more easily? And indeed, the thing could be repaired wheread an IG helemt must be discarded when there's a hole in the bowl.
So you could be right there, but we'd need to test it. But for sure there was a reason why the Roman army adopted these Persian-style helmets.

I'm also unsure that shortage of materials, or money, was a reason for the change in helmet design. If the late Roman state wanted to churn out massive quantities of simple infantry helmets, they could surely have gone back to something like the Montefortino or Coolus design, which were produced in enormous numbers to equip the armies of the civil war era of the later 1st century BC. I don't believe that technologies and techniques were somehow 'lost' or forgotten, by Romans or anybody else; if the late Romans turned to (quite complicated) riveted composite helmets, they did so because these helmets suited their needs better.

Of course I can't be sure, but I think the change in production coincided with a change in the organisation of the fabricae? One would think that a lot of people producing one part makes for a more flexible production (no shortage of parts means no delays) while the production of one whole Imperial Gallic helmet takes up more time. That goes for a Coolus as well - the bowl has to be hammered from one piece, even if it's more simple than an IG. The technology would never have been a problem, they could handle that indeed.
No, not a money problem (I never said that did I? Didn't mean to if I did).