The lore of old suggests blade points being broken off to keep crew from stabbing one another but the actual use is much more mundane. In a pitching sea a pointed blade is dangerous in tall ship rigging and even on a modern yacht. Usually set up with a lanyard so the rigging knife can be kept from falling from the rigging and hitting someone below.
In fact custom rigging knives come in folding knives and fixed blade selections. A modified Sheep foot pattern blade and a marlinespike (a tool for pulling apart knots) in the case of folders. With a handmade fixed blade knife a marlinespike is an extra tool. This needs to be fitted with the knife sheath to provide easy anchoring of the knife and the spike. in heavy seas. As convenient as folding knives are, its hard to deploy a spike and blade with one hand. The straight blade typically found in rigging knives provides a very rigid blade designed to cut through the thickest of rope, or line.