When next year's fawn begins inside a doe, there's a delay before the fertilized egg implants itself in the uterus. One guess might be that over dozens of millennia, this delay evolved so that pronghorns could rut early, leaving time to recover before winter.
Pronghorn metabolisms burn faster than a deer's, and much faster than an elk's.
The bucks rut themselves jerky-thin, and the does need time to recover from raising fawns, and neither has the bulk of deer or elk to protect them from January winds that blow like frozen fire across the flats. Their early rut grants pronghorns a recovery cruise before the green forbs along the creeks and waterholes dry up, before snow covers everything but the tallest sage. But all of this is mere bio-speak. Yes, the horn-hunter's dollars sustain local economies and help ensure the survival of wild game. But no horn hunter I have ever known, no matter how passionate, has the same regard for a deer or antelope as the Inuit of the North have for caribou, or the Bushmen of the Kalahari have for gemsbok.