> Why does Rust use "let"?

let is the standard keyword for introducing a new, shadowing variable binding. It is a very old tradition and is immediately recognizable to functional programmers.

> If you want easy adoptation from one of the two largest languages in the world, change what matters and stick with the rest.

In the case of "let", it would be a false consistency with C/Java. Assignment in C/Java does not have the same semantics as a let binding in Rust, although a let binding in Rust has very similar semantics to a let binding in Scheme or Haskell.