What are the reasons some Muslims do not fast during Ramadan?

There are two reasons that I can think of, why some Muslims do not fast during Ramadan. First, if they are not in good health it might not be medically advisable, and medical necessity is more urgent than ritual observance. Secondly, they just may not be that observant. There are also lots of Jews who eat non-kosher food, and Catholics who do not fast during Lent, for similar reasons.