The phrase "it has more to do with..." supports and emphasizes the main properties of a subject, it does not separate the main property from other properties. When you say "I like the restaurant, but it has more to do with the staff," the subject is your opinion of the restaurant. With this sentence you are saying that, while many factors go into evaluating the quality of a restaurant (i.e food, decor, choices, etc.), you like the restaurant mostly because of the staff.
If you didn't like anything about the restaurant, you would say, "the restaurant was not good, but my opinion has more to do with the staff than anything else." If you liked the food, though, you wouldn't use, 'it has more to do with'. Remember, 'it has more to do with' emphasizes a property, it does not separate it from other properties. You would want to say, "the restaurant was good, but I did not like the staff."