Because here in the "Theory, Composing, and Sound Design" forum, we recognize the pursuit of knowledge in music as a worthwhile endeavor in its own right, as well as something important for the budding composer/song-writer/producer/beat-maker to understand in relation to his or her own compositions and productions.
What is usually called the hook (but not always, as the term is sometimes used loosely) is also called the "chorus" or "refrain" in traditional composition terms. In an actual "song" (something that is sung or has lyrics, rather than purely instrumental), the chorus is the part that is repeated, often (but not always) also the name of the song. The part you remember.
While I'm pretty sure that the OP already knows this, it's important to note because there is also usually a corresponding repetition in the rhythm and the harmony; a repeated section that fits with the chorus/refrain every time.
If the OP is having difficulty identifying the chorus, it could be because he/she is not yet accustomed to hearing it, but it could also be because he/she is listening to bad productions with poor composition and song structure, so the refrain is not evident.