this justifies the library's existence but does not justify it's inclusion upstream.
Re:Rails API is coming to Rails 5
by 1qaz2wsx3edc on Tuesday April 21, 2015 @01:38PM
(#9415672)
Because Rails has become bloatware and has been since they lost sight of the future of the web and stagnated on innovating...
EDIT: sorry, I mis-read your post. This is just "Why Rails and not Sinatra," not "this is easy enough to do on its own, why bother."
I wasn't directly involved in the decision, so I cant' tell you, to be honest.