After spending a majority of my playtime (Around 150 Minecraft days) in a snow covered biome(snowy tundra) I have noticed that no Wandering Traders have spawned. This is apparent as there are no trader llamas near me/ in the biome. After venturing away from there and into a nearby desert a Wandering Trader had spawned only after a couple of days had passed. This has led me to believe that Wandering Traders are unable to spawn in these snowy biomes, possibly due to the snow layers preventing them from doing so.