We got pretty comfortable with the commodities the Rails environment provides, so it's understandable some people would rather just add another layer (Backbone/Spine) and avoid the paradigm shift.
The advantages of attacking new problems with a new toolkit can sometimes appear less beneficial, because swapping out the current mega-stack for something slimmer inevitably leads to reduction in features (ie.: You end up making another `view` in place of a collection partial. Mailer, gems/middle-wares, etc..)
That said, despite getting pretty comfortable with Rails/Backbone|Spine, I'm in the pragmatic camp, looking forward to tackling a few side-projects with Meteor.