system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are nursery rhymes so morbid?

In Jack and Jill, Jack cracked his skull open.

In Rock-a-bye baby, a baby fell out of a tree. 

Ring Around the Rosie is based on the bubonic plague, which wiped out 1/3 of the entire European population!

In It's Raining, It's Pouring, an old man bumped his head and died.

3 blind mice got their tails chopped off with a knife.
gpt
Some nursery rhymes are meant to teach moral lessons, others were a product of a society that was much more prone to morbid events and therefore psychologically influenced and drawn to them. Ring around the rosie for example as you mention was made during a time when people were fixated on death. It was not just in poems, but also in art, songs, and in the general attitude of everyday life. In short, morbid messages in poems tend to reflect how society felt at large.