We're talking about learning C/C++ from scratch which makes no sense to do by using a decades old book because it wouldn't teach you any modern features. Also we're not talking about computer science.
Some people want to use them, they are useful in some contexts and they often already exist in some form elsewhere, but the majority of people often do not need them.
That said, when you learn a foreign language, you do not learn every word in the dictionary and every grammatical structure. The same is true for programming. You just don't need to have a more up to date book than one on C89 to begin learning C.
