You were told to write about whatever interests you — and your essays went nowhere.
That's the writer's definition of an essay; the reader's is different — it only works if it helps a specific reader understand something they already want to understand well.
So the topic has to be theirs, not yours; the goal is understanding, not action; and the value has to be proven by argument.
So what actually makes something an essay?
That it helps a specific reader understand something better that they already want to understand well.
Pick a topic that's theirs, not yours; aim for understanding, not action; know where they stand so you can take them further; and give them a real argument — claim, evidence, and the warrant between.
A new idea isn't knowledge until a reader accepts it, so the reader is the batter, not the icing.