Plus it's hard to find a lot of mix and match sets to create diverse glamour.
I wouldn't expect advancement all in one step - glamour 'progression' exists even for those fashion outliers:
(1. Match the clothing - some taste is required here. First, it's about shape and style. A clean outline vs. more bulk. Then, if you're good, you can even match material types ( cloth vs. leather vs glossy etc. ) Marketboard investigation and retaining set pieces that may have potential down the road is advised.
(2. Gear that is dyed appropriately. Again, some taste is required - but a general rule is that metallics are pretty tasteless on most things.
(3. If possible, glamour an appropriate weapon that complements the set and look you're going for.
Personnaly, i not meet a player having exacly the same mix like me. Its rare if there is someone. I meet sometime the same outfit of my crafter outfit only .
With how they have the fitting room window right now where you can try on multiple pieces does help with putting together the perfect look. Just need to find the right pices that work with each other, and with 3.5 we will also be able to pre-view the outfit using dyes.
As much as I'd like to mix n match different armor pieces lots of them just don't look right together and even if they do the colour scheme is usually off even when dyed since the shade of (insert colour here) depends on the piece of gear and it's texture. It's just easier to go with sets that are designed to go together basically. Sets that aren't armor are a tad easier to manage but not all of us want that aesthetic.
Could be a lot of reasons
1) they like it
2) its cheap on marketboard
3) they don't have enough creativity to come up with unique mix&match/dye-wise outfit
Idk. It personally bothers me when I see someone else wearing the same armor as me. I think it has to do with the fact that my glamour is an outlet for my creativity, and if it's not unique, it's no longer "me."
But other people might not have that same qualm. I can respect that (so long as they don't then copy my awesome look for themselves).
Let them stay generic, I'll look even more beautiful in comparison.
If only dungeon sets were dyeable.
Some things are just flat out popular. The Thavnairian Bustier set is still all the rage on my server and it's part of why I get so annoyed about glamour gender locks - one of the most popular looks everyone adores is a constant reminder of the situation. Personally I prefer reasonably unusual glamours but I keep popular pieces lying around for dressing up in too.