I guess most posts are based on experience or lack of.

Not all cold winter areas have snow. Picture high desert areas. The only water you have is the water you carry with you. One winter setting up a hunt camp the fifty gallon plastic drum of water froze solid before we could get the tent set up and heated. I thawed it out with two white gas lanterns while it was still inside my trucks canopy, but it took awhile. Usually a thermos is to small or if large, to heavy to carry enough water to hunt all day. Our hunting party always carries multiple old military stainless steel canteens or stainless steel bottles. Even with insulated covers after a long day most are partially or totally frozen. So heating by a warming fire is common. Melting snow, where available, is both time and fuel consuming and if done to fast can scorch the pot and taste nasty. Most SS canteens and bottles are narrow mouth which limits their use to drinking only and can be difficult to clean. These newer wide mouth SS bottles are more versatile.

The only plastic water containers I carry now are bladders but they just augment the SS canteens or bottles.