This keeps getting brought up, and I feel people are completely oblivious to the fact that immersion would be just as awful with the ability to disable everyone's glams.
Some of the default armour is hideous, and some of the best gear sets do not fit their respective jobs.
For example, the previous tier of Eden gear, for all casters and healers, was a frickin' night gown.
Without glamours, you'd have thousands of Hrothgars, male Roegadyn, Highlanders, etc. all strutting around in frilly night gowns and tights. Which is fine... but it's certainly no less immersion breaking.