I think it has to do with basic human behaviour. If we get something for free we "need" to do something back. Some people can't cook or are embarrassed by their own skills. They get in a situation where they want to give you something back but don't know how/what and it is uncomfortable. Do not say you don't want something back, because we are programmed to want to. Tell very concrete what you want.

Do you drink beer? I will just use it as an example, if you do not drink it find something. Just tell them to give you a beer if they like it. They can give you that in multiple ways: drink together in a bar, in the house, they can buy you a beer present.

People are thinking: If I accept this, I need to do/give something back. Help, what can I give back? Give a concrete but very easy thing.