The 116 allowed chainguides to be fitted using the lockrings to secure back in the days before ISCG. Shimano had launched the DH XTR Groupset and they were aware that the majority of riders would use backplate designs....
The MRP, Mr Dirt, DMR and Evil / E13 backing plates were 3-5mm thick and if you had a 112 BB you could find youself running out of thread before it was fully home which resulted in stripped bb treads (I know this first hand) so the 116 option was preferred. Many DH bikes of the era moved from 68 to 73 to 83 to 100 or anywhere inbetween - pity if you have a Giant team DH fro m04 with a 100mm bb.....
I supidly sold my 112 and bought at crazy expense a 116 fromCRC while they still ahd them - should have bought 2!