This is how it's been, at least since 2nd edition in the '90s.
Low-level druids are still mastering the "nature" of the Prime Material - learning to summon animals and draw on their aspects to enhance themselves. But 4th and 5th level spells are beyond that introductory phase. This is where you learn to manipulate the very building blocks of all nature - life energy and the elemental forces, as well as complex natural phenomena like diseases and disasters. You still get some plant and animal related spells, but they're generally bigger in scope - summoning hordes or granting complete control over animals. You also expand your control over nature to less "natural" monsters with spells like charm monster.
In much older editions of DnD, 9th level was considered "name level" - this is the point where you are your own political force to be reckoned with. Lords and armies in the areas you're active have standing policies for you specifically, usually "placate if possible", and you're known across at least your continent, if not further. On a meta level, it's also traditionally the point where "pure casters" like wizards and clerics are expected to surpass normal encounter design. At this point you can skip entire adventure arcs using spells like fly and teleport. The Druid's 5th level spells are equally game-changing: you can raise the dead, undo permanent disabilities like petrification, make plants and animals have human-level intellects, wipe out an entire village or cripple a town with a single insect summoning, bind a person to complete a quest, or permanently reshape the land.
