They're both different types of stories. TLA was a quest/adventure story that took the characters all over the world, while LoK appears to be of a smaller scale, with only Republic City being the primary focus. With the story focusing on just one locale rather than the fate of the entire world (for now, at least), it makes sense to me that there isn't as much of a sense of urgency as there was for the TLA gang. At this point, Korra's just trying to learn airbending while adapting to life in Republic City. She doesn't have a global threat looming over her head right now, like Aang did from the moment he woke up.