The dry sump system usually had a pretty big oil tank compared to the oil pan capacity of the wet sump system. Often three or more times as much oil.
I suspect all of this kept oil cooler (at a time when oil quality was generally worse than today), avoided in the engine splashing and foaming, oil pick-up problems in cornering, and provided a good oil reservoir if oil consumption/leakage during a race was an issue.
I owned a 1961 Norton motorcycle that was dry sump, and a 1972 Honda 4 cylinder 750 cc motorcycle that was also dry sump.