Originally, RT was more or less a 'good faith' measurement of the general sentiment\quality of a film, but it is so easily manipulated it was inevitable that it would become meaningless.
While they definitely measure on different metrics, the goal of a critic is supposed to be to measure films worth watching (even if only for a subset of the total audience). When 95% of critics tell you to see a movie that only 10% of people enjoy, something's broken.
40 million people not paid to review movies seem to hate this movie; but the 100 people who love it are both A) paid to watch it and B) seem to entirely fit the vast minority of viewers who like it.