Movies about fictional scientists and politicians work. Why don't their biopics?

Ahhh, biopics. Biopics are one of the few genres of movie that avoid all the problems I outlined in my prior post, as they are meant to tell a mostly true story. "Based on a true story" is one of those phrases that can make a film seem particularly artsy on the poster, right along "independent", "foreign", and "nominated for X Insert Name Here Awards". Some biopics can turn out good, but unfortunately most seem to have their fair share of problems, even ones which are critically acclaimed. The thing that makes this especially problematic is that movies that do not claim to be based on a true story but have the same situations (i.e science, politics, drama) often do work, According to me, at least, the problems "artsy" biopics have (and why non-biopics often don't have these problems) are:

• Not being accurate. Of course, "based on a true story" doesn't mean "is a true story", so these films can get away with this somewhat. However, if something seems fishy to the audience and it turns out to be inaccurate, the audience may feel somewhat duped. Of course, inaccuracy makes it hard to explain the following problem:
• Being too cliché/ oversimplifying the truth. Say that you're watching a movie about a real boxer, and according to the movie, this boxer was a small-time fighter with a heart of gold and a love interest, until he was picked to fight in the big leagues. One training montage later, you realize, "Hey, this is just Rocky but with some real boxer's name slapped on it!" This example is made up, but it could easily happen. (It may have happened already.) If the main character was in a romance, expect romantic comedy tropes. If a character is from an oppressed group, expect them to overcome their problems. More generally, the main character will be a hero whose flaws only (paradoxically) make him more likable. (This can be especially problematic as it can make real pioneers seem less special.) If all hope is lost with 10 minutes to go, miracles will happen. The list goes on. These tropes might seem bad in a fictional film, but if the film is supposed to be real, especially if it begs for an Oscar, there is less of an excuse. 
• Clunky historical/academic exposition.  Say that you want to make a movie about the Human Genome Project. Obviously (at least if you're Hollywood) you don't expect the audience to kmow much about how DNA, and don't want to pause the plot, so you have Venter or Collins explain their methods to their colleagues. (And you don't know who I'm talking about, you're the reason why.) Trouble is, why would an scientist need to know basic biology? These scenes can make it harder to suspend disbelief.
• Trying to tell a message without the necessary subtlety. 
• Foreshadowing/historical in-jokes. 
• Adding unnecessary plot points.
• Counting on its artsy reputation to excuse the problems above.

This post is incomplete, as I was too lazy to write on the rest of the points. I might suggest some fixes in my next post.