fpco decided to do their own thing instead of contributing to that effort.
Your timeline is way off. The initial announcement for what would become Stackage was posted in 2012, a full three years before the post you linked was authored (and a year before Cabal got sandboxes!). The proposal blog post doesn't even mention diverging from
cabal at all, and the official way to use stackage was through cabal sandboxes. The first public beta of
stack was announced in June 2015, and according to the blog post, FPCo had been working on
stack internally for about a year before that. If these timelines are to be believed, then
stack was six months into internal produ