Don't tell me ~ "I don't share my recipe"!!!!

A new pet peeve.  When people "won't share a recipe".  What's with that?  Are they seriously afraid you'll make it better then them? Afraid you'll market it and they won't get the credit? It always boggles my mind - why people are like that?  I have ALWAYS shared every recipe - if someone likes something - I'm proud of it and happy to share so they can make it, and if they've made a change to it or any improvement - please tell me about it - I want to know too!  Is it their ego?  It actually happens quite frequently... at first I think they are joking "I don't share this recipe".... seriously, how did you make it - then I realize - they ARE serious, they DON'T share the recipe!!!  And let's be honest... I doubt it's an original recipe, how many of your famous creations are totally original?  I don't think ANY of mine are... and I admit it!