I mean, don't get me wrong - one hears that working at Apple, Google, FB, etc is the sh*t. But at a certain point, the whole process is analogous to the dating world. A person can play hard-to-get and make you jump through a string of hoops, but after a while, the interested party will inevitably reach the point where they realize their own self-worth and quit wasting their time.
A company that puts candidates through a huge number of interview rounds begins to give the message that "the Company doesn't respect you - we're much more important." And at a certain point, the really capable candidates will have too much else on their plate to continue chasing after an opportunity that never seems any closer to bearing fruit.