While the DLC Pack 1 for Breath of the Wild is 2 days away from dropping for those of us in Western audiences, in Japan its 1 day away and new information has arrived!
According to the updated Japanese website for The Legend of Zelda: Breath of the Wild, while DLC Pack The Master Trials only requires 456 MB of free space to download on the Switch, it requires 3.7 GB on Wii U.
It has not officially been revealed why the numbers are what they are, but rest assured he Wii U version is not getting more content with the DLC than the Switch version is, it’s just more likely that the Switch has better and more advanced file compression than the Wii U does.
Source: nintendo.jp