Because new commons are always released during an event. It's best to get them during an event before they are half priced for the duration of the event before becoming regular items once the event has ended.

You'll be able to earn "event currency/tokens" to spend when you talk during the event - it's like getting free items. But a lot of people choose to spend all their gold on the new items they didn't get with the tokens because it is so cheap just for that duration!