It’s not a utopia at all, it’s a dystopia. The ship they are on was built buy the mega-corp Buy N’ Large, which according to Pixar in the lore, gained a total monopoly over not just all other companies on earth, but much of the world governments.
It’s a classic Cyberpunk trope of mega-corps that effectively are the government because they wield so much power and influence.
Plus, socialism is a society where the workers own the means of production, which isn’t the case in the movie, so it can’t be socialist.