It can be, but it isn't always. The reason for the presumption of innocence combined with the proof beyond a reasonable doubt standard in criminal trials is a judgement about the desirability of the particular effects that can be expected with and without that principal.
It cannot automatically be assumed that those considerations generalize to other contexts -- they must be considered in each context.
In the broader context, like in the legal context, it's not a claim about what is true, but rather a claim about what we should believe (or more appropriately, how we should treat the accused) given the evidence we have. You don't say "this person definitely didn't commit a crime, because we don't have evidence," but rather "we don't consider this person guilty, and thus don't punish him or her, until we get some evidence."
It cannot automatically be assumed that those considerations generalize to other contexts -- they must be considered in each context.