One of the key reasons Rust took this approach is because Rust's implementation is zero cost - it doesn't require a runtime to implement. It is potentially very efficient, and thanks to Rust's other guarantees its very safe to use. It's as close to bare metal as you can get for a async framework and as a result its incredibly efficient.

However, to me, the implementation is a lot complex that green threads. The Future's crate has had a lot of churn, and when I first dabbled in it a while back, it was one of the first few times I struggled to understand what the compiler errors even meant as the types were so deep. Compared to golang's 'go', futures are harder to understand, plus you have to rewrite all your networking/blocking code to be compatible (Python would still likely have to do the same, but I think it could be done in such a way that if you were using the system provided networking libraries, you could get compatibility for "free").

Python doesn't benefit from the Rust benefits explained in that article. Python already has a garbage collector and runtime. Python is single threaded.

I don't follow the Python language to have a well informed opinion on why they went with futures, but I doubt its close to the reasoning that Rust chose.