Why offer with stipulations???

Okay, so I am totally confused. I thought when you offered to do something nice for someone, that's what it was. A gesture to show your support, and love for the person you are offering your niceness to. Why then do people offer to do nice things but with strings attached? I cannot figure it out. I have never offered to do something for someone, and then tried to control it, regulate it, and tell them how and when they can have it. I am so freakin irritated right now. I mean how dumb is that?? WHY OFFER AT ALL?!??!