Well a customizer is responsible for each unit he or she creates. So every piece I make, I make damn sure it works as best I can make it.
Neca is responsible for thousands of units going out and that requires a workforce that can mass produce the figures for the cheapest amount of money possible.
For example, I've only bought two Neca Preds so far, a Wolf and a Big Red. The Big Red's sword holding hands don't come near fitting, they just fall right out. Also his left hip ball had some glue drip in the joint and is fused in one position. A customizer, a good one anyhow, would never let a piece ship like that. And these are simple things that shouldn't have been allowed. A helmet and face that line up is much trickier. Unless the helmet is oversized or the face in undersized. Now a customizer could do it. But mass producing something like that... maybe... but the price per unit would probably go way up. (Strong magnets -- like the ones in Sideshow boxes -- might work for that, but strong magnets are expensive to add in these circumstances.)
But I'm with you, I love removable helmets. It's the whole transformational bit.