Remember when 2.0 first came out and every event had a vendor that sold rewards from the 1.0 events? Why can't we get that for each subsequent event?
Although I have never seen the Devs respond to the event furnishings issue, I'm sure that their response to the Calamity Salvager idea is that they would love to do it, but can't do to memory limitations.
There couldn't possibly be any technical issues with simply having an NPC sell old event items at each new event. There should be an NPC selling Eastern Cherry Trees and Crimson Felt Mats for gil right next to the NPC who is selling current event gear/furnishings for tokens.