Games Manual, which is like how to play this game?
I don't think it carries any importance, it might be just a one time thing and almost every gamblers has idea of how the games works because basically those casino games are very simple and even for the one who doesn't can learn from a google search and if want better presentations there are tons of videos out there to check out.
What I would love to add them is the demo feature, which exactly does what you suggesting but in a lot better way.
I agree. Also the idea that a gambler won't be engaging oneself to a game he doesn't know how things work. In most instances, you are just placing your bet so I guess there's no need for such thing. Demo feature on the other hand is already present with some platforms wherein demo accounts are used to give initial impression to new players on how a platform feels once they actually transition into it. Problem only is that with demo accounts, win rates are higher which causes confusion to some players once they play on real time.
Casinos are out for business, i.e they are out to make money from gamblers who feel they win money from the casino. This is why they will not give you any instructional material for you to have advantage over them. Casinos only provide demo games for you to practice, band have knowledge on the game, so that you can be motivated to bet or gain back your gambling appetite. It is you that will generate gambling materials and set rules for yourself in order for you not to gamble irresponsibly and become addicted. Casinos don't care about what happens to you, if you are addicted or not but only after your money.
No that's not it I guess. Casinos are already earning from each of the transactions and there's no need for them to take advantage of their player's ignorance of the games 'coz if that's so they should have just rig the games in the first place. It is just the idea that it will consume their time doing so, for something or concern that is not a representative of all gamblers. Ofcourse every gambler is expected to know things especially mechanics of a game.