Except that you can because it is all hearsay with no direct first hand knowledge and there are already people willing to testify, under oath, that a lot of it didn't happen.
So yeah, it's easy to ignore .. or laugh at it really... when it's one-sided hearsay from someone that had no first hand knowledge.
In this case me or you repeating it is hearsay. But what's being shared in the trial (is it a trial? I don't know what this really is) isn't all hearsay. A lot of what's being shared, under oath, is first hand knowledge. The people sharing these stories worked directly with the President, and most of what they are sharing was their personal experience.
To your point unless they can prove their stories, who knows what's really true. I don't doubt there's people testifying that want to paint him in as bad of light as possible, but I doubt anyone's sitting in front of the grand jury and intentionally testifying something they know is false. Even if you assume some are, it's hard to believe every claim is.