Here is my theory on what happened to Freeman...based on a gut hunch and not much more.
I think the real sand in the Vaseline was Winfield. Frazier probably really wanted Winny back and Spielman made the call to move on. He then signed with SEA for less money and didn't make the team, and if I recall correctly, Frazier kept saying things in the media like, "We're keeping in touch," and "We're still talking to Antoine." But, Speilman wanted to keep a little cap space for emergency mid-season pickups while Frazier still wanted Winny back...
When Spielman dropped that 3+ mil on Freeman Frazier got extremely pissed off because that money could have gone to Winny and helped the team much, much more than bringin in a 3rd string scrap heap QB. At that point in the season it was already painfully obvious that we were missing our nickel back, and I'm guessing, the writing was on the wall as far as Leslie keeping the job going forward.
Which led to Frazier making his point on Monday Night Football for better or worse for everybody involved.
I think the end it came down to something much simpler - work ethic. We know that Freeman had a history of poor work ethic, and I think that the starting job was his for the taking, but he just didn't have the work ethic to put in the effort and hours required. He WAS coming into an offense very late in the game, but instead of that being an excuse it means you need to work harder to catch up - something that I just don't see Freeman doing.
His horrible performance against the Giants was the partially the result of being put in early, but I think it had much more to do with what he was, or more importantly, was NOT doing in the weeks and months leading up to that game.