[2111USMC]

Looking at the picture in the link, it doesn’t look like a jacket to me. It looks like a jacket liner.

[Redcitizen]

If it gets cold enough, people would use it as a jacket liner for the jacket. In cool temps, thats when people may want to wear it as outerwear.

[Newbomb Turk]

It's a fleece outerwear. It's just the wrong size. Truth be told, when the fleece was first issued it was black and had no name tag or rank insignia areas and was designed for under your uniform. But if your uniforms fit properly there was not enough room to pull it over the fleece.

Commanders quickly just told troops to wear them as outerwear, relying on your headgear to identify your rank.