people that don't share recipes... why?

what's the deal with that?

whenever i cook something and someone wants the recipe i gladly hand it over. secret ingrediants, whatever.

this is also in the same vein as " i won't give you the recipe so you have to figure itout and it makes you a better cook". why not give the recipe and let them make it like you make it then chamge itup if they feel the need?