People like to find a way to shut off their brains and "outsource" their decision-making to others. Then they can blame the "other" if things go wrong too. Rotten Tomatoes is just a popular way to do it for movies.
For myself, I'll admit it's a factor, but "trusted" reviewers (people that you find agree with your own preferences more often than not) are the best IMO. I have about 3 people I check and see what they think. They MOSTLY agree, and they MOSTLY agree with me, but I need to go through the effort to see why they don't agree with me. There's a few specific movies that 1 or 2 of them hate, but I think are great, or at the least it's a "It's fine, nothing wrong with it, and entertaining, but glad I didn't pay the money to see it in theatres, but not a bad movie either."
For myself, I'll admit it's a factor, but "trusted" reviewers (people that you find agree with your own preferences more often than not) are the best IMO. I have about 3 people I check and see what they think. They MOSTLY agree, and they MOSTLY agree with me, but I need to go through the effort to see why they don't agree with me. There's a few specific movies that 1 or 2 of them hate, but I think are great, or at the least it's a "It's fine, nothing wrong with it, and entertaining, but glad I didn't pay the money to see it in theatres, but not a bad movie either."