Thanos is simply larger than life.
Director James Gunn had a dilemma on bringing Thanos for an appearance in “Guardians of the Galaxy.” With Ronan the Accuser being the Guardians’ primary adversary, Thanos shouldn’t overshadow the villainous role in the film.
“You’re setting up this gigantic character that, in one way, isn’t really a part of your movie,” he explained to Vulture. “His presence doesn’t really serve being in Guardians, and having Thanos be in that scene was more helpful to the Marvel universe than it was to Guardians of the Galaxy. I always wanted to have Thanos in there, but from a structural standpoint, you don’t need him.”
Thanos ended up being in the film to witness Ronan’s defiance by killing the Other in front of him.
“We’ve had the Other, who’s obviously very powerful even in comparison to Loki, and then we see Ronan wipe his ass with him,” he said. “So that I liked, but even that was sort of difficult, because it played as funnier when I first wrote it, and the humor didn’t work so much.”
It worked out better in the end anyways. Thanos will be a much bigger adversary to the Avengers and Guardians of the Galaxy in the future.