How come Disney's films are always over rated in IMDB?

Rating: 6/10 (17 May 2018)

Similar to Star Wars : The Last Jedi, Avengers : Infinity War is, IMHO, vastly over rated at the current 8.8. In terms of mindless actions and visual/sound effects its first rate, but on almost every other aspects as a movie its just terrible, and I will not repeat as a lot of the recent reviews here have covered these.
What I really want to say is it seems to be a trend for Disney to kill the main heroes in a franchise (Luke Skywalker and the various heroes here) just to "surprise" the audience and as a means to draw them back to the squeal to see whether they will be revived. This is a cheap trick. If the movie is good enough you don't cheap tricks to boost box office.
The other things is, call me old fashioned, but a fantasy movie should make us happy. The heroes should always win at the end. I mean, if I need to see an invincible villain in action all I need is to watch political leaders on CNN!