That's because most books assume that you're playing serious poker against serious, knowledgeable and experienced players. The reality is that in most low stakes games (ESPECIALLY
freerolls), the other players will often call your AA overbet pre-flop, or all-in 3-bet w/ any low pair, and any AX. Flush chasers will often call pretty much any bet with any two suited cards.
It very much depends on the stakes and the level of play. Freerolls are the loosest (even looser than play money). The higher the stakes, the more serious, knowledgeable and experienced the players, and hence the more applicable the book's teachings.