In article , C J Campbell
wrote:

Either that or there is some FAA reg that involves runways of greater than
5000' that the designers wanted to take advantage of. But even there the reg
probably is based on the biggest runway you can fit on a section.

I haven't looked recently, but it would be contained in Part 150.
I do know that 7000 foot runway is considered transport category, so I
suspect that insurance companies may require certain aircraft to be
operated from runways greater than x-thousand feet.