[reallyreason]

It really depends on the abstraction model of the library. If the library needs to actually read/write a file, it either needs to depend on a runtime or provide some horrific abstraction over the process it will use to do that. This doesn't apply to sync IO libraries which can just use the Standard Library.

Web/server frameworks have to bind to a runtime because they have to make decisions about how to connect to a socket. Hyper is sufficiently abstract that it doesn't require any runtime, but using hyper directly provides no framework-like benefits and requires that you make those decisions and provide a compatible socket-like implementation for sending requests.

[surajrmal]

That's the thing though, it's possible but it makes the simple hello world example more tedious. It's totally possible to make an abstraction layer, provide a tokio implementation out of the box but leave the door open for other implementations to slot in. Anyone who's written portable code for non posix systems is used to this experience. Standardization is definitely better but it also has its own share problems as it can limit what's possible. I expect that the decision to delay standardizing on these interfaces too early will end up leading to a better long term design. Especially if major improvements to async are on the horizon and can alter the final shape of that standard.