My theory is that most "Undecided" voters aren't really torn between trump OR biden as much as they clearly prefer one but may simply not vote due to general disgust/apathy/unwillingness to stand in line if they procrastinated enough not to vote early.
I think the advantage that biden will have is that, barring some unforeseen event, he will start out with a much higher "bank" of dependable votes. The thing is, I don't think people are too invested yet in trump's trials etc. But once we are knee deep into the summer and he's STILL losing lawsuits, getting shyt on etc, I just don't see him attracting people who want to see that type of circus for the next 4 years.