The film is a story designed to invoke a childlike sense of wonder, and harken back the feeling of literally playing with monster trucks as a kid.
It also seems worth pointing out that a movie like Monster Trucks simply seems like a ton of fun.
It’s the story of two high school students (Lucas Till and Jane Levy) who discover a subterranean creature who can power a truck.
Considering the amount of nostalgia that Jane Levy went into the production of the film with, that thematic idea probably felt right up her alley from the very beginning.