If you were actually following the storyline of the quest, you would know that the mount you actually get as the reward is notreally the same mount you use during the quest, as you end up destroying that one by burning it to save the child - the 'Great Pumpkin' from the previous All Saints Wakes (in disguise as the Pumpkin Headed Apparition) brings it back 'from the heavens' as a token of thanks for it's sacrifice). In other words, a very subtle and benign use of the 'came back wrong' trope.
So thus it makes sense from that perspective why the mount reward does not have that Bewitched themed ability, as fun as it is.
Also the Magitek Armour can actually not use it's weapons immediately after finishing the 2.0 storyline - you have to do a sidequest with the Garlond Ironworks to repair the weapon systems to gain that functionality back (and even then, they're still damaged in that the abilities are only glamour and don't actually do any damage).
I can only speculate that it probably would take time to code a 'passive' version of the ability into the game which the development team just didn't have (after all, 3.1's development and the transfer of the Chaos data centre to Europe has been taking up the majority of SE's development time at the moment so an ultimately superfluous glamour ability for a seasonal event reward would naturally end up way down the bottom of SE's priorities at the moment. That's not to say they won't change it later. But try and look at it from their perspective too (players were naturally demanding SE run this event ASAP so no matter what they do it's wrong).
Hengen mentioned the reason for this above - the Armorie actually requires SE to physically add items to the Armorie's database so that you can store them in there, which they do very infrequently (there's still event items from a couple of years ago that cannot be stored in the Armorie). It should also be noted that the Armorie tends to only be used for items that cannot be easily dyed or are stated as being unsellable or 'unique/untradeable'. The new Halloween gear is dyeable and can be sold at the Market Board. Hence, no Armorie Storage for these items.
Having said that, storing them is a bit of a problem for those like me who tend to be hoarders (I had to junk a whole heap of stuff of my retainer to find the space to store them, so I definitely sympathize with you.).