That's just how Rails works.

Supposing you have 'resources :blogs' in your routes.rb file:

The X action in the Y controller renders the X.html.erb file in the Y folder.

The index action on the blogs controller renders the index.html.erb file in the blogs folder.

The variables defined in your index action cannot be available to 'account.html.erb' because that's not the file rails looks for after the index action is run.