https://www.gamespot.com/articles/the-new-overwatch-skins-are-rare-but-loot-box-odds/1100-6456322/

With its latest update, Blizzard answered a common complaint among Overwatch fans. Rather than release new items that can only be obtained for a limited time through an event-specific loot box, it added more than 100 new cosmetics into the standard loot box. That means there's no big hurry to unlock everything--but it also means you're left hoping for a lucky drop from a loot box that contains a lot of stuff.