Given that a lot of games in recent years also offer alternate or custom control schemes, there is no reason to consult an instruction manual which gives you a default control scheme that you might not even use anyway.
Manuals used to give details about the plot of the game, the main character and the enemies you'll be facing, all of which you can just get in mission briefings or cutscenes anyway. Programming credits are already viewable in the game. No need to see them in print.
The varying game modes are pretty self-explanatory. If you have trouble figuring out the meaning of "Multiplayer", "Time Trial" or "Campaign" without the manual, I probably don't want you doing my income taxes for me and I don't want you dating my daughter either.