Essentially, the attraction is being able to wait for multiple things at the same time within a single thread. It's useful for things like webservers that want to handle thousands of connections simultaneously, but most of these connections aren't actually doing anything useful, they are waiting on the filesystem or the database connection or some other network service. And you can't really spawn thousands of OS threads because those have non-trivial overhead.

Now, you may think this can be done in C with the `select()` API and many switch statements. And you would be correct. All these "async" languages and framework are wrappers around this that let you write your code in a procedural manner, and take care of the select and switch for you.