Winter tyres, such as Uniroyal MS 77 Plus or Snow Max 2, have deeper tread depths which are designed to allow dry snow to pack into their treads. This packed snow actually helps improve traction and snow-on-snow friction in deep snow.
It all comes down to the fact that the freezing points and melting points of ice are related to both temperature and pressure. If you think of it like a snowball, you can put pressure on the snow and it creates an ice-bond. When a tyre holds a lot of snow, the same thing happens, making it good for traction when a tyre holds a lot of snow in its tread.
Meanwhile, sipes – tiny channels cut into the tread blocks - allow water, slush and thin snow to be broken up and dispersed. When the tyre rotates these sipes are pressed into the snow. As the tyre flexes, its sipes open up and grab snow and ice, biting them into tiny pieces.