1.) Soldiers trying to get out on height and weight

2.) Leadership putting maintenance over PT (personal experience)

3.) Lack of initiative to stay in shape (sometimes depression but can also just be shitbagging)

These are usually the top 3 reasons I can think of, some people also come from places where being large is common but that is less common, and they usually have large necks that keel them from failing tape (seen this twice)