he was already found by the jury to have sexually assaulted her via EITHER penetration of his finger or his penis. They just could not state for sure which and thus the sexual assault finding.
Had there been semen on her dress, then the jury could use that infer it was his penis and found the rape to be the crime he committed.
And Trump lying about her does matter, as you say he has some type of sexual interaction with her but just does not want to admit it. That lie, you accept, is something a jury can use to determine credibility and who is lying about the rape he did.