It's pretty much familiarity. If I'd learned Rust back in the day, I'd probably not want to learn C++ for syntax reasons as well.
One thing I think Rust gets wrong is classes. I absolutely don't understand why you would require a separate `impl` block to provide methods. C++ has a reasonable syntax of providing methods in the class.
Well, they're not classes, they're interfaces, and so you can implement multiple interfaces for multiple types, and so you have to implement them separately from the type declaration. There's not too much of a way around that, I think.
