Why do level 4 and 5 Druid spells seem to change tone?

I am playing a Druid for the first time (D&D 5e) and am quite enjoying it. My character recently hit level 9, and I noticed that the 4th and 5th level spells seem to shift in tone dramatically from earlier levels.

While lower level spells seem to emphasize beasts and nature thematically, the higher level spells seem to shift toward elementals and life force / necromancy style spells. Is there a reason for this?

In other words, is there lore behind the shift in tone and theme?

Or is there a tactical reason for this shift?

Or am I imagining things?