They had to do it and everybody does it.

If you want to reincarnate Spock, and you want Nimoy to play him, you've got to make up some whacky reason for a baby to become an adult in a few hours. If you want some alien threat to be scary because of its reproductive rate, and you want the story to be resolvable in a short period of story time (Hellboy, Alien, etc.) then you have the bad guys reach adult-hood within minutes of hatching. If you want cockroachs to evolve to look like humans within a story arc, you have to postulate that evolution works pretty much instantly (Mimic). There was an enterprise episode where Clint/Flip/Skippy/what's-his-name the engineer was sort of cloned, but they had to postulate the silly instant maturity to make the plot work. I'm sure you can come up with a few examples of this same time-compression trick without trying too hard.

Bottom line: it is a literary gimmick. (or leftist ploy, you be the judge)