A triangular shaped bayonet creates a wound that can’t not be easily repaired, so the recipient usually bleeds to death. They were outlawed by the Geneva Convention, and apparently TR.
At the time, it was believed that the bayonet was declining as a viable battlefield implement, and would only be used for “light duty” like guarding prisoners.
TR, in his usual hands-on manner, used a standard Krag rifle with bayonet to demonstrate that the “rod-bayonet” of the early Springfields would easily be broken off in battle...his written statement to his generals was that he believed the rod bayonet “...about as bad an invention as I ever saw”.
One heck of a lot of SKS rifles came with a spike bayonet. The 91-30 Nagants did, too.