The grand jury is not a trial. There are no defense lawyers, no cross examinations, nobody to object to what is being said, and no judge to sustain or over rule any objections. In a GJ they only hear one side of a case which is the prosecutors, hence the saying you can indict a ham sandwich.
It's not until a trial where the defendants team is allowed to examine the prosecutors evidence, point out the flaws and lies, and then present their evidence. In an actual trial, the defense is allowed to object to lines of questioning, cross examine their witnesses, and bring in their own witnesses.
We don't know what was said in the Trump GJ case. But given Fat Alvin is a complete sleeze ball, we can only imagine.
For instance Fat Alvin could have told the GJ jury he has a star witness that was Trump's attorney. What the jurors may not have known is that Cohen is a habitual liar looking for a break, he's a convicted perjurer, and even told his own lawyer that Trump knew nothing about the payment to Stormy. None of that can come out until the actual trial unless we get a non-biased judge to throw the case out.