First, for all who might not know it: Hitting puberty, most uncut boys experience that smegma can build up and accumulate quite fast and easy especially in this stage of life. This effect is said to be caused amongst others by hormonal adjustments of the body itself as well as penile growth processes. Furthermore, especially in early puberty, most boys tend to being not too interested in personal hygiene, showering etc. (which of cause changes again when they discover that girls feel more attracted to well-manicured and well-smelling boys ;-) ). Also some teenagers still have a rather untrained / more or less long and tight foreskin and a very sensitive glans, and skinning back sometimes can cause discomfort, pain or (in best case) erections (which can be embarrasing and disturbing when happening in the wrong moment, e.g. in public showers). So it's a natural thing that some teenage boys try to avoid pulling back their foreskins whenever possible.
In the age of 13 I had to stay in hospital due to an unidentified illness. When a rather young doctor examined me from head to toe, she also did it “down there”. My foreskin still used to be quite long and “medium tight” those days (however not too tight to be pulled back completely with some effort at least when my penis was flaccid). The doctor pushed my foreskin back as far as ever possible. After my glans had been popped all out, there was a visible portion of smegma showing up. Still holding my foreskin painfully back, she told me that it was still too tight, and obviously this was resulting in hygiene issues, and that circumcision would cure this problem. I was deeply frightened, and from that day on, always expected to become cut.
Needless to say that the overall scenario was severely embarassing for me (not only but amongst others also because of the obvious hygienic issue).
In retrospect I am not sure if the young doctor's suggestion to have me circumcised (this is how I interpreted her words back than) maybe also had been influenced by the fact that she had discovered smegma under my foreskin.