Because being in the presence of popular people is a major accomplishment, right? Far greater an accomplishment than the defense of any original PhD thesis, right?
I can drive to the Viceroy hotel bar right now and be in the presence of a random A-list celebrity if I so choose. By your logic, that act alone sets me worlds apart from the entire body of original research being done by PhD candidates all over the world.
I will never understand the nature of being starstruck. If I want to shut down my rational faculty, I have a bottle of Glenkinchie at the ready.