Well, as an engineer, I don't like to assume anything "back in the day." I know the physics didn't change but I wasn't there so I hesitate to say for sure what someone was thinking for the design.
We're all familiar with the "3-bolt" cams vs 1-bolt. The 3-bolts were used on the more radical cams. Again, I assume the engineers decided they needed increased clampload for the harmonics associated with the bigger lobes so they went to 3 bolts to get that added clampload/friction.
I'll share this: for the crank damper joint (which also uses a key for location), there are highly complex models/calculations run to come up with a calculated value that has to meet a spec to insure the damper joint will not move. Again, the bolt supplies the clampload and the joint is then held tight by friction.
Some of you may have disassembled a modern engine and found a "gritty" washer between such a joint. We call those "diamond washers" as they are impregnated with diamond dust/chips to enhance friction and thus the integrity of the joint. You engineer things to NOT need them (unnecessary cost) but sometimes field data or a challenging design forces you to add them. FWIW