I never know why people complain about this. I've had a manual in every new game I've bought over the last couple of years and they still have everything the old ones do (granted that isn't many because I tend to buy used). A bit of backstory, info on basic gameplay elements, handwaving of bugs or bad design (from dying from running too fast in Sonic is a diabolical trap set by Dr. Robotnik to the Animus 2.0 fixing a "bug" that made you instantly drown when you touched water in Assassin's Creed). And even cute little comics in games like Ace Attorney!
Maybe we're just buying different games