"Because, surprise! These movies are not documentaries, nor are they acts of journalism. (And even documentaries don’t always need to be totally accurate — just ask Werner Herzog.) They’re narrative works, and just like any other narrative work, they need to be true to themselves — to the demands of drama, to the demands of (yes) entertainment, and even to the demands of the broader truths they’re trying to evoke."
If that is the case it is quite simple to just change the names of the people involved and don't make the claim "Based on true events" because the ONLY reason a film does that is to fool the prospective viewer into believing she will see THE TRUE EVENTS! It is wrong.