The short answer is that Congress was worried about the optics. Honestly, I don't blame them so much for that, if they would be honest about it.
Plenty of great stuff came out in the hearing. Normally, I would has skipped over the Democrats. Almost did after the first Democrat to give an opening statement said exactly what I expected: Trump! Trump, Trump, Trump! Trumpity, Trumpity, Trump, Trump!
But the second Democrat said something I don't remember from the Jan 6th show trial: Acting Secretary of Defense Christopher Miller stated that Trump had indeed requested ten thousand National Guard troops to protect the capital. But Miller ignored that request, dismissing it as "Trump banter." 17:00
Anyone who has ever been a military officer knows that a commander's requests are considered orders. There is no wiggle room. Specificallly, my officers basic manual ruled out taking phrases like "I want," or "I desire," as requests. It is unthinkable that a defense secretary who had ever worn a uniform thought it was OK to think that a presidential order could be irrelevant "banter."