In order to keep drivers as busy as possible while also keeping ETAs low for passengers, requests are dispatched to the driver who will arrive soonest. When you drop off a passenger, it's likely that your next request will be close by.
If you've dropped someone off and have been waiting for a longer period of time, the chances of your next request being further away increase. This is all in the interest of keeping you busy and maximizing earnings! Metrics such as ratings, acceptance, or cancellation rates do not factor into whether or not you receive a request.