Anyone know why this occurs? Or like most things, just natural?
It's been discussed in various threads. Some of the difference is variation in normal anatomy, but probably much more is a sequela from circumcision. The standard normal anatomy of the meatus from childhood through adulthood includes slightly plump "lips" that press together to close off the meatus when a man is not urinating or cumming. The meatal lips are the culmination of the raphe that runs from the anus across the perinæum, over the middle of the scrotum, right up the underside of the penis (the "seam") and becomes the frenulum. The frenulum usually leads directly into the meatal lips.
Circumcision affects the meatus in two basic ways: abrasion and blood supply. When the frenulum is ablated or cut in infancy or early childhood, it interferes with continued support and development of the meatus. And an early permanently-exposed glans rubs constantly against diapers and clothing and comes in direct contact with diaper ammonia and fecal matter. Most often this results in repeated irritation and eventual
meatal stenosis, or narrowing of the meatal orifice. This is when the boy's penile lips shrink or disappear and the slit becomes more of a hole.
If you look at the photos here on LPSG, about 90% of the intact guys have a closed slit and mild or prominent meatal lips. About 3 in 4 of the childhood-circumcised guys have an open meatus that is anywhere from 20 to 50% smaller than the lips-slit when opened.
Guys with the natural slit generally have a more powerful urine stream than guys with a hole that's a consequence of stenosis. And that's significant, because less urinary reflux means better urethral/bladder health and fewer UTIs. It's preferable to void completely and effectively. As I've said before, I can often guess if the guy at the urinal next to me is uncut because he pisses like a fuckin' firehose. A much smaller percentage of cut guys do, too, but most have a less powerful exit of urine. As a general rule, the later the circumcision the closer to natural the meatus and urine stream is.