I've only played about a half dozen MMOs myself, and this is the only MMO where a repeated event with a mat turn-in system has the mats destroyed every year before the event repeats. It is even inconsistent with their own other events -- Crystal Cove, Festivault, Midwinter, and Anniversary are all mat turn-in systems that don't expire. It is simply the better way to do things as it allows long time players to heavily play or relax from year to year with none of the time they spent on the event wasted. The concept of an event being all or nothing is just dumb... it should be allowed for casual fun where people can earn a bit here or there along with those that do heavy grinds. The fact that they sell items in the store for real money to get stuff they'll just delete on you if you were unable to spend it immediately is another black mark.
I had a death of a close friend come up during the last event, and I'm having 20+ hours worth of key and mat grinding just disappear because life came and I was unable to turn in. It illustrates yet another reason to not have mats expire, but I've asked for it every year even when I had no mats to lose. This outlier case shouldn't exist, and I think is bad for the event itself.
Yes, it is true that the mats clearly stated that they would expire. No one here is saying that "wow, this came out of nowhere!" People are wanting it to change. Where else are they going to ask but here on the forums? And canceled subscriptions is a way that people try to put monetary reasons to pay attention. Though people have asked for them to stop the expiration BS each year since they introduced Night Revels in 2015, and people canceled subscriptions over it last year as well. Losing a couple hundred bucks a year is not make or break for them, so such actions is rather pointless. I just hope that at some point a dev will see the reasons, go "why not" and fix it.