Turanil said:Anyway, what prevents a DM to ask the players that they read the campaign setting book?
DM's can ask. If the campaign setting book costs money it comes down to the DM saying "All of you go out and spend $35 on this book and read it." If your DM is kind enough to give you a handout of all the pertinent information that takes care of the money issue, but very few people will sit there and create a campaign booklet for their players.
Getting the people to read it once they have it is another thing. Not everyone has the time or the inclination to spend hours and hours reading a book for the campaign. Some people are casual gamers and don't have the time to put into reading one sourcebook for a game, let alone all the possible ones you could be using for your game.
Things you can do...when you are talking about some country, add in something like "....which is the country directly north of the coutry you are in...divided by a great wall of mountains.." or"...the country with which your country is at war with and has been at war with for the pasy 100 years...". Some people just forget the details of things.