People have no inate understanding of 'menu'. We don't even read short words like that letter by letter, it's read as a block and is far more complex than three bars.
"Menu" has a consistent meaning (a list of items to choose from) which most people can be assumed to know. Icons aren't as easily parsed and take more of a mental load to reason about them. Or just trial and error to figure them out.
And if we want to focus on just three bars let's not leave out the skeuomorphism trend where three bars meant the "grip" area, something to use to rearrange items or windows.
This is true. It means "exactly the same" where it was used millions of times before it landed on a computer: https://en.wikipedia.org/wiki/Triple_bar