I should probably just keep my trap shut since I’m not any of the above. However, from the best I can ascertain, the answer to your question is: that’s the way God designed the plant, or if you prefer, the way it evolved.
Most trees will grow over a particular geographic area, but will thrive more in one area of that region than the rest. A thriving plant is converting sunlight and CO2 to sugars faster than a sickly one. Some trees thrive in cooler wetter conditions, some in warmer areas, some in clay, some in sand, some in low PH, some near neutral.
There is a bible (of sort) about trees written by a guy now at UofG; Michael Dirr that most nurserymen reference when wondering the culture of any tree in North America. It’s called “Manual of Woody Landscape Plants”. The thing is over 1100 pages long and contains a wealth of info about nearly all the trees that live in North America. He often states the conditions a given species prefers, or thrives in, but don’t say WHY. I think the WHY is a function of the genetic code.
Dirr says Sourwood prefer acid, peaty, well drained soils.