Windows does offer an official API for this, as the article states. Unfortunately, everyone wants an API that works exactly like epoll, and IOCP just Doesn't Work Like That. It's actually way closer to how most people would expect async I/O to work, were they to design it from scratch without the well being poisoned by knowledge of epoll.

However, every *nix / macOS person writes their epoll code, then finds out that it Doesn't Work That Way on Windows, so this gives them back their epoll-like API.

From a Windows development point of view, Linux is way behind. Async I/O has been at the core of the NT kernel since the very beginning (since VMS, even), whereas on Linux (and Unix) everything has been designed with blocking I/O in mind. IOCP match the way people usually think about asynchronous processing, but people have just become used to the weird way poll and epoll do things. It's like saying Windows is behind Linux because it doesn't support Unix permissions.