While I used Tera as an example (and big offender) I've seen this happen in almost all MMORPGs, and specially on cash shop items.

It's popular to cross real world events like Christmas and Valentines with in-game events, and even if we don't  count how bad this is for the lore, it fills the game with all kinda of silly gear.

Later you are fighting that old god bent to destroy all life in the planet and suddently your tank jumps around wearing a santa costume while wielding a lolipop as a shield.

I mean, why bother even creating a lore and a setting if you won't rape it that hard? How they expect me to care about their quest, their heroes and their story when the developers themselves doesn't seen to?