The internal wiring to light up the bolt and gauntlets turned out to be too thin and would break so that had to be updated with a new system and so on.
The early gauntlets restricted Zac’s hand movement too much.
Like some of you have seen in early pics the boots were originally very different but those were falling apart and had to be redesigned.
And once you nail down the design, the material and all other details you then have to make multiples and ones for stunts etc. Even during shooting you have to do upgrades.