Another possible reason for Guardians of the Galaxy Vol. 3 being different is because James Gunn has stated before that the third and final film will go a long way in setting up phase 4 of the Marvel Cinematic Universe, which definitely sounds like a reason for the project to be more complex and a lot different from the other two Guardians movies.
In addition to saying that Guardians of the Galaxy Vol. 3 will be more complex, Gunn also revealed that it’s going to be pretty different from the previous two Guardians movies.
Everything leading up to Guardians of the Galaxy Vol. 3 has been pretty heavy so far and now, director James Gunn has revealed that the third and final installment will be “more complex” and “very different” than the previous two.
These new elements in Guardians of the Galaxy Vol. 3 could be from the death of Gamora in Infinity War.