A good film critic should tell his readers if they are likely to enjoy the film.
Right?
We buy your publication or spend time on your website hoping it will help us. If you tell me something is a good movie, I want to go believing that you are right, that it will indeed entertain me, that it is value for my money and time.
I don't care for your opinion if it isn't helping me spend my money and time wisely.
It's far simpler to tell others whether you liked a movie, than to predict how it will do at the box office (i. e. how much the aam junta will like it). If you have that special skill, you deserve to advise me and get paid for it.