system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If Butter is just churned Cream. Why does Cream go bad very quickly, but Butter lasts a long time?

Butter can sit out on the counter for ages. I've never actually seen butter go bad.

But Cream, if you leave that on the counter for a day or two it starts to smell.
gpt
When you churn cream, the butterfat separates from the buttermilk.  So the butter isn't all of the cream, just the butterfat part, with much less water content.  It's the buttermilk part that ferments.