Originally Posted by
Eurhetemec
I think it's got to be down to the former.
Most other MMOs already sell a ton of transmog-equivalent outfits. Guild Wars 2 has countless, vastly outnumbering the "legit" outfits/armours you can get (last I played anyway), ESO has a bunch, FFXIV has dozens and dozens despite being sub-based like WoW, SWTOR I can't find a good list for, but they certainly had a bunch at one point.
WoW is actually really weird among MMORPGs that it doesn't sell tons of transmog-type outfits. Hopefully it stays that way. I suspect it will because at this point, changing that and regularly selling costumes, especially ones that compared favourably with in-game stuff would be unlikely to be well-received.
Are you saying that's true right now? Because that definitely isn't true right now. Whilst any model used in-game is bound to get recolours (because why not?), where shop models tend to be unique models (albeit rarely unique animations), there are certainly tons and tons of extremely cool mounts in-game, and the shop mounts aren't devastatingly cool (indeed most are a bit silly).