cargo run --example exaple_name causes "no example target named 'example_name'"

Question

I am studying the following code and cannot wrap my head around why cargo run --example abigen wouldn't work. The docs state that package has to be specified like so cargo run -p ethers --example abigen. Indeed, this fixes the issue. But according to Rust docs, I should be able to use the first version. Why doesn't this first version work?