I’m not trying to sound jaded. I’m just trying to tell people that maybe a more PC centric approach to playing their PC might be a better mindset than a “what’s the next plot point I need to hit?”
Your point is laudable. I guess I'm the contrarian here, but I think you're going about it all wrong.
One of the hardest jobs a GM has is his effort to motivate players. The GM is akin to a film director, and he's charged with finding ways to get his actors to perform the way he needs them to.
In my current campaign, I created a sandbox for my players to explore. And, I created this elaborate background for the PC's describing their culture, the local history, and their family legacy. Man, it was so "cool". I thought to myself, "They're going to be begging me for the next part of this."
I decided to send out the "history" in parts in e-mails to the players in between games. I thought: What better way to do this? Each player will come to the game knowing what his player knows, and we won't take game time to go over this stuff. Plus, it's so "cool" that they'll eat it up like a breathtaking novel.
Guess what. I got to the game, and hardly anybody had read their stuff. I was peeved. I had spent a long time on that, and I was expecting what compliments on how "cool" I had made the game world.
It became a point of contention between me, the GM, and the players. I broke the background up into small, easy-to-read chunks, and then sent those out. It still didn't help. The players avoided it like reading the instructions to their DVR.
Then, I stumbled across Justin Alexander's web site and read his article about feeding lore to players. He says that, no matter how "cool" it is, players don't want to read that stuff. They like it when they know it--they just don't want to spend any time (even a minute) reading it. If you're lucky, the best a player will do is skim the material, even if its written better than Stephen King ever thought about putting word to paper.
I thought about what Justin had to say, and I realized (remembered--this is one of those things I knew and forgot) that it wasn't the players that were failing--IT WAS ME!
I was failing at motiviating my players to be interested in the background material. I wasn't presenting it in the right format for it to be appreciated.
Justin provides many ideas for presenting lore to players in a manner to which they will respond.
And, that's my point to you. I see what you're trying to do, I just don't think you're going about it the right way.
You need, imo, to find a different way to motivate your players to play characters and immerse themselves in your world rather than systematically playing the game like a computer rpg.
I don't think a letter (which, I've found, they'll just skim anyways!) berating them is going to do the trick.