2.1 "The Future Trait" introduces a confusing (to me) example

[LighthouseJ]

I was sort of familiar with async/await, enough to get into trouble and decided to finally read the async book from the start and really understand it or at least gain a better understanding.

I totally got the Rust-specific parts about purpose of poll(), what the Output type was, etc... I got to 2.1, and for discussion, it introduces SimpleFuture as a boiled-down version of the real Future trait, but it confused me because it was a copy of the real Future trait, but why wasn't (at least excerpts) from Future used instead?

I write C++ actively daily too and I'm familiar with its "named requirements" (https://en.cppreference.com/w/cpp/named_req) which are an informal collection of methods that must be implemented to satisfy a specific interface. These collections may be considered something of a trait. I got confused because I didn't know if I could use any trait I wanted to make as long as it has an "Output" type, and a poll function?

Can this section be modified to add caveats to clear up what the role of SimpleFuture is and that readers should use the real Future, or just show readers snippets from the real Future trait altogether?