Look at the original
Clone Commander Cody. That figure came across looking like a pinhead. Now, compare that with the remade
Commander Cody figure from the Vintage Collection, and you'll see a noticeably larger helmet. The Airborne Trooper you cited looks good, but it's a completely different helmet design from the standard phase II armor's helmet.
There may be some other issues at work here. Notably the toy safety standards that came to light with toys produced in China in the past few years. Those issues ranged from hazardous paints to potential choking hazards. And a small accessory like a helmet might have been seen as one of those hazards. Additionally, these standards might also dictate the grade of plastic that can be used in an item like a helmet. A more rigid plastic might make for a helmet that looks more film accurate, but might not put the design in compliance with child safety standards. I'm certainly not trying to apologize for Hasbro. But this sort of criteria likely seems to be at work.
I think the better option is to go with something along the lines of the CW Obi-Wan Kenobi you mentioned: 2 seperate heads that are interchangeable. But in that case Hasbro is going to be dealing with slightly more expensive tooling, and we the consumers, are going to have to eat that cost increase at some point.