Fans should not expect a full-fledged Thanos backstory in 'Avengers: Infinity War.' The Russos revealed in an interview that the Big Bad's history was cut as it is not important to the overarching story.
The Russo Brothers are about to embark on the 'Avengers: Infinity War' press tours where they will show footage from the film. They have asked fans who will be at the event to keep spoilers to themselves.