Before I started developing Rails I always used JSON + client side templates which were constructed in pure jQuery and really tedious.
Then, with Rails, I asked myself, why would I want to have the template somewhere in the middle of a JS file where it isn't even recognizable as an HTML template at first sight? Why not have it, like all the other views, in one convenient place? Furthermore, often you have a partial you render on the server side and with some AJAX you send more entities of this partial to the client. Having this partial twice is really tedious if you wan't to tweak the HTML.
Then, with Rails, I asked myself, why would I want to have the template somewhere in the middle of a JS file where it isn't even recognizable as an HTML template at first sight? Why not have it, like all the other views, in one convenient place? Furthermore, often you have a partial you render on the server side and with some AJAX you send more entities of this partial to the client. Having this partial twice is really tedious if you wan't to tweak the HTML.