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.