I guess because StackExchange has higher Google ranking and allows comments, easy edits, supports latex etc. It's a great platform for stuff like this.

Also, the langdev SE is still in beta, and pretty early beta at that; posting useful material there helps get it off the ground. That said, I wouldn't be surprised if Alexis also posts it to her blog at some point.

The person who wrote this [1] seems to be a Haskell (GHC) contributor and someone hailing from lexi-lambda.

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[1] https://langdev.stackexchange.com/users/861/alexis-king

I, too, hail from myself.

Oops. For some reason I confused lexi-lambda (which I didn't know) with lambda-the-ultimate (http://lambda-the-ultimate.org).