[Rails] define_method vs module_eval

Rails code:

Accessors.send :define_method, :"default_#{name}", &block

Accessors.module_eval <<-METHOD, __FILE__, __LINE__ + 1
   def #{name}
   @details.fetch(:#{name}, [])
   end

   def #{name}=(value)
   value = value.present? ? Array(value) : default_#{name}
   _set_detail(:#{name}, value) if value != @details[:#{name}]
   end

   remove_possible_method :initialize_details
   def initialize_details(details)
   #{initialize.join("\n")}
   end
   METHOD
end

Here we invoke send() on the module Accessors, passing
the :define_method symbol, which represents the define_method private
method available from Class class. We create an instance method called
default_locale, whose value is the block passed from register_detail
class method of ActionView::LookupContext. Note that we later use
"include Accessors" within LookupContext class to make that available
as an instance method of LookupContext. We then create more instance
methods using module_eval, with here-documents to specify our
delimiter (METHOD) and the dynamic constants (__FILE__, __LINE__) for
accurate error reporting on stacktrace. My question is why not include
default_#{name} as part of the evaluated string in module_eval, rather
than invoking send() directly above that using define_method?

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