The top box office films in 2018 all have got huge fanbases and are well known as a lot of them are a part of a franchise.
Due to this, most of them have a huge budget which allows more advertisements to be produced, causing more people to become aware of the film and therefore feel more inclined to watch them, expecting the film to be of good quality.
Along with this a lot of the films are family friendly which makes more people watch them as there’s little to no age restriction on most the films, animated films especially sell more tickets as parents go with their kids [double the tickets].