Perhaps it is even simpler than bots and hacking, maybe it is just human nature.
For example, when BvS or Suicide Squad were trashed on RT, people who likewise thought those movies were garbage had no issue with the score and felt the scores were justified, but a few die hard fans cried foul with the rating system. Now the situation is reversed, a film that you (whoever you may be) like has received a low RT rating so it must be the work of a treacherous conspiracy to bring down Star Wars and therefore the score cannot possibly be accurate.
The rating system is only right when it is in agreement with how you feel about a particular film…after all how can your opinion possibly be wrong (just ask my wife😀, she’s never wrong). It is truly subjective. But the bigger question is, Who the hell cares? Why should it bother anyone how any site or system rates a movie? If you like it, great, enjoy your film; if you don’t, great, don’t watch it…and everyone lived happily ever after.