Uh, maybe they changed it (Tactics made the change to looser fitting cloth suits first) because spandex is the most illogical choice in the world for an all-purpose utility suit that will need to be passed down for generations and possibly repaired several times? I thought all the painted pictures of characters in the original vault suits looked a little too comic-booky or alternately, like they belonged a heavy metal album cover. It was just weird.
With no linkable source and scarce recollection, consider this hypothetical for the moment... I always assumed that the vault suits were auto-weaved and/or extruded on demand by the vault systems. Would not some device be installed to supply vault suits on demand; (and possibly just incinerate them rather than use water to clean them)?
(I mean, these things could have actually been made from a combination of gels and plastics, and fabricated on the spot with a custom fit by a big' ol clunky vault suit making machine).