People say that the rationale for requiring unanimous jury decisions is rooted in favouritism of the defendant. But is that true? Without referencing certain game theoretic experiments/models, it seems unusually unfair to require that all jurors vote "not guilty" in order to be acquitted. If a minority of jurors believes in the accused's innocence, it seems like the unanimity requirement may push this minority towards voting "guilty" despite their beliefs.
The question to be answered is "did the state prove guilt beyond reasonable doubt", the answer to which should have no reasonable doubt. The interests of the defendant are sufficiently protected by the basic burden of proof requirement. The alternative that a single vote of not guilty exonerates the defendant would seriously hobble the interests of the people, and the alternative of automatic mistrial would make trials prohibitively expensive. The unanimity requirement does mean that in case of initial disagreement, parties have to re-think their positions, which is not a bad thing.
The question of whethar a supermajority of guilty votes suffices for conviction was decided in a recent case, Ramos v. Louisiana, allowing conviction with a 10-2 vote. The court takes unanimity to be a basic common law right from the 14th century. Louisiana and Oregon had unconventional schemes allowing less than unanimous decisions: the reasoning behind the unanimity requirement is discussed extensively in that opinion. Since Alito, Roberts and Kagan dissented in part, the rationale for the other view is also spelled out.