It’s an expression. You don’t really win them by “exploring”, but by “playing the game”. You end a match? Lootbox. You played 3 days in a row! Lootbox. You opened the options screen? Lootbox.

They usually have a very involved opening animation with music and sounds specifically designed to maximize the feeling of anticipation. Once you see it it feels completely different from what you are describing, because it’s so obviously trying to maximize the gambling aspect of it. It’s like confusing genuine love with prostitution.