LogFAQs > #980120767

I'd need specific examples to give more specific answers, but in general it's because the length of the time skip they used was what made sense to them for the story they were trying to tell. Since you brought up that you are watching a show that does this, I'll also add that when it comes to live action shows/movies (although since you didn't specify, I don't know if the show you're referring to is live action or not), there's also the practical concern of having characters age significantly more than the actors portraying them.