I was wondering why not use bolts too. I had to look them up. The spirol pins (coiled spring pins) are not like a shear pin, so I don't know that they will break any quicker or later than a bolt? They are designed to flex, provide uniform strength and not come loose due to vibration. Very interesting little piece of engineering.
https://www.spirol.com/library/sub_c...enefits_us.pdf