That doesn't apply outside of the legal system, and it doesn't even apply to all players in a courtroom. Certainly the DA that filed charges thinks the defendant is guilty.
People like you and me are free to judge by our own standards. I think that most of us found O.J. Simpson guilty of murder and Bill Cosby guilty of date rape even though neither was found guilty of those crimes formally.
How about Nixon? Was he guilty? Once again, not formally. He just quit his job and went home a free man but I'd hazard a guess that most informed observers found him guilty.
Another important distinction between a formal judge or juror and somebody outside of the process is that we have more verdicts available to us, including probably guilty and probably innocent. Innocent is apparently not an option in court. Available verdicts as I understand it are guilty, not guilty, or no verdict (hung jury/mistrial).
And finally, we are free to change our verdicts if additional evidence suggests that we should. We don't need to wait for the process to play out before making tentative judgments.
My position is that Trump is very probably guilty of criminal activity given what we know about his character and the incredible number revelations in just six months. What criminal activity is he guilty of? We don't know just what yet. He may be guilty of collusion with the Russians, obstruction of justice, emoluments violations, and/or money laundering.
If he is, we don't yet know which combination of crimes he has committed, and we sure don't know if he'll ever be held accountable for any of them if guilty. But I for one have seen enough already to judge that the Trump family is probably a criminal enterprise. I see societal parasites with a sense of entitlement and no respect for the rule of law or fair play.