Mimicing is a birds natural way of communicating with its flockmates. Every day you hear wild birds calling to one another. This is the basis on which we motivate our birds to speak to us. Although birds do most often learn to speak the words and phrases we use most frequently, the repetition is based upon the fact that the words are uttered often as a part of the birds emotional environment. This is because, quite simply, they're easier .
Some words attract their ear, some are just easier to reproduce.
However, rest assured, once your parrot is motivated to speak to you, and gets a big response for doing so, new words are just around the corner. Quakers usually begin talking between 3-6 months of age. One of the most frequently first reproduced human sounds is kissing. Quakers will often practice their human sounds at low volume and often their early attempts will be misconstrued as 'noise'. Don't discourage your parrot from noise making if you want a well enunciated parrot later on.