[ricardobeat]

Ryan Dahl in February 2010, when Promises were removed from core:

    Because many people (myself included) only want a low-level interface
    to file system operations that does not necessitate creating an
    object, while many other people want something like promises but
    different in one way or another. So instead of promises we'll use last
    argument callbacks and consign the task of building better abstraction
    layers to user libraries.

Those libraries do exist. There still isn't a canonical Promises specification. Node trying to force promises onto the ecosystem early on would've been like applying brakes and slow down adoption enormously.

[mjackson]

> There still isn't a canonical Promises specification.

Yes, there is: https://github.com/promises-aplus/promises-spec

[ricardobeat]

Promises/A+ surfaced less than 6 months ago, and is not implemented by most widely-used frameworks. Still a bit far from canonical.

[tlrobinson]

Promises/A+ is just a more fully specified version of Promises/A, which has been around for about 4 years.