Cats are extremely smart animals and have realised that their humans have absolutely no idea about body language and pheremones as a means of communicating across species. So what did cats do? They noticed that human beings talk in order to express themselves, and thus adapted their behaviour to communicate with us by meowing.
If you don’t believe this, try and remember the last time you saw two cats meowing at each other for an extended period of time!
Some breeds of cat are more vocal than others, especially oriental breeds like Siamese.