You don't understand how the production process works. Before 3.0 hit while they were working on job adjustments, they considered the idea of adding more egis on top of what was already there, but they realized if they did that it would just create useless clutter, that's why SMN is the way it is now because of those changes.

The egi glamour is most likely an idea they came up with near the release of 3.0/later in the process but what you seem to be missing from their explanation is they don't want to half ass it. They could easily makea single skin and be done but instead they want to go the whole 9 yards. They want to make the skin, the unique animations, the unique sounds and effects and potentially unique names for abilities when using certain glamour egis. While they will of course offer no change in the abilities being used the idea is to offer more visual changes than for example Ramuh that still uses the Garuda animations for actions.