It's because people have a limited amount of time in a day and they likely wouldn't want to repeat the foundations of their position to everyone they meet.

This is why we divide sets of ideas into schools of thought so that we can build on them instead of starting from scratch. Kind of like SDK's for ideas to which we can add our own creative thinking.

Also, repeated questions in a private conversation makes sense, but in public, it can give the other person suspicion that you are doing it just to put their ideas down in front of other people, even if you do it in good faith.