Why close-in weapon systems use different gun arrangements

Why do many close-in weapon systems prefer one rotary cannon over several separate guns?

The choice depends chiefly on ammunition supply and logistics, and some navies still prefer multiple-gun arrangements.

Aircraft-gun convergence does not by itself explain the popularity of one rotary cannon in many close-in systems. National design practice also matters. Russian systems, for example, use multiple-gun arrangements. Ammunition supply and the logistics of carrying and feeding enough rounds are more important than applying a single fighter-gun rule to every CIWS.