Wayne — It is a "standard" adopted by architects, owners and others. That's all. Fortunately it is challenged by many here, and others.
Here is some reading for you on the subject:
On early golf courses, the variables that made up the routing were often quirky. The order of par and length of holes were not established to follow any idea of good formula, nor was any extreme effort taken to make sure these variables seemed perfect. The ideals of ensuring pattern, balance, and symmetry were not as important as allowing the land to unfold the routing. The routing was a product of the land and came to life as places were found to fit holes. Unlike modern times, where routings are very often contrived and purposefully balanced and symmetric, ancient and early designs were whatever they became. There being no concept of par most certainly influenced some of these layouts. Holes were short, long, or somewhere in between. One example of such a course comes to mind that, if routed and designed today, might, unfortunately, get people fired from their jobs.
Bishop Auckland, is a charming 18-hole layout in Northern England. The Bishop, as it is known, sports a most unpredictable order of par. Beginning on the front side, golfers face holes of modern-day par 4, 5, 5, 5, 3, 4, 3, 3, 5 = 37, and, continuing on the back, par 3, 5, 3, 4, 4, 4, 4, 4, 4 = 35. There is simply nothing “usual” about how Bishop Auckland is routed, the order of the pars, or balance between the nines. Amazingly, in the club’s centennial book (1894 to 1994), there is zilch about how in the world this design oddity came to be. The rationales, however, can be gleaned by inspecting The Bishop firsthand. Quite simply — and appropriately — this is a course where the land was used to its fullest. Short holes (par 3s) were obviously situated along a meandering creek, and because the creek refused to run uphill to the clubhouse site, these holes are largely bunched in one area, well away from the clubhouse. From there, the puzzle became one of getting away from the clubhouse and back again. The reason there are three par 5s in a row is that the most important thing was not answering to a developer or banker about what would make a good course or whether it would be laughed at by the critics. Rather, the only requirement was that the golf fit — and that it be good and challenging in the process. If you look at the scorecard, it might seem that The Bishop ends on a boring note. How can six par 4s possibly make for a good finish? Well, when you build a course on the sloping moorlands above a valley, you get uphill and downhill and sidehill holes and all sorts of combinations of each. The Bishop’s architects realized this. The order of par and everything else unusual about this course is a product of what mattered most. Remember, too, that James Kay, the original designer, and those who followed were not encumbered by the whole idea of par. Bishop Auckland fits, but sadly it would be a difficult task to convince the modern-day developer of this.