In a nutshell, Rails doesn't eager load models (or anything else) when running rake tasks on Production.
The simplest way to work with a model is to require
it when you begin the rake task, and it should work as expected, in this case:
# explicitly require model
require 'application_wide_setting'
It's possible to eager load the entire rails app with:
Rails.application.eager_load!
However, you may have issues with some initializers (ie. devise)