Innocence is the default setting. It's like being considered alive rather than dead. Sure, there are some people who are probably dead, but until such time a doctor says they are - we have to presume they're legally alive. Until Trump is tried and convicted he is legally innocent and that's the neutral state of being. Whether someone does something or not seems to me to be an irrelevance to the legal state.
You're right, there are guilty people in prison who haven't done anything and there are innocent people on the outside who almost certainly have - that's a travesty of legal justice... but we cannot act on our feelings on that matter when making law. We can appeal the court to re-examine the evidence (and we should) and I agree the court doesn't determine reality, but it does determine legal reality and therefore the state of innocence and guilt. That is what is being questioned. That and the sanity of the American people. ;o)