What did sheep do before there were humans around to give them haircuts?
No I-dear (oh wait, we’re talking sheep not deer)
Speculating, though... perhaps sheep are similar to pure breed canines, where over millennia their genetic characteristics were crafted by humans - in the case of sheep, to maximize wool production while diminishing their natural ability to shed and/or slow down its growth.
A lot of the more primitive breeds of sheep either don’t grow wool, or else shed their wool naturally. They look more like goats than sheep.