The trial was Schiff standing and telling lies about what he had presented in writing and what he could make up on the spot followed by the Presidents attorneys.
No where in the process do Senators become beat cops, forensic experts, jailers, or attorneys representing either side.
Schiff was the prosecution. He was answered by the defense. Now is the jury supposed to ask for new witnesses, new detectives assigned to investigate all over again from the beginning, and otherwise demand that what the prosecution and defense presented be declared deficient? No, Schiff had his chance to put anyone he wanted to in the witness stand and that was in the House.
There have been 13 Senate impeachment trials. This would be the first without witnesses.
But if you say so...