I suppose it's because if you were to say 'you're not using plates', you'd be talking about plates in general, but if you said 'the plates', you'd be talking about some specific plates, I don't know, like... The plates I gave you as a wedding present. How come you're not using the plates?
Well, imho, even if in English the Dutch phoneme for ui doesn't exist, I think that the RP phoneme /ɜː/ (as in 'fur', /fɜː /) is a good approximation.
I haven't received any negative feedback about it from my partner (Flemish native speaker) nor from my tutor (Netherlands Dutch native speaker).
I suppose that as you become more familiar with the language, are more exposed to it and gain confidence, you won't need such 'proxy', as I like to call it ;)
There is no sound in English similar to the Dutch ui, hence it cannot be compared to English. Perhaps this website will help: http://www.heardutchhere.net/DutchPronunciation.html#UI