Is there a reason why configuration files options are commented instead of set to false in many systems?

Question

I was wondering why it seems to be a convention to comment options in configuration files instead of setting them to false.

In most cases, instead of having an option like that :

#This an option to enable something
enable_something=NO

It will be :

#This is an option to enable something
#enable_something=YES

I'm not really sure what are the benefits of this. To be honest in my opinion, it seems harder to find commented options in a file.