They are not and have not ever been intended to be a harbinger of who will win an election, though they have been used as such in media and by pollsters who have padded the bottom line by touting predictive questions. They are a tool for post-election demographic analysis, which is why they are performed in waves and true-upped to official results after results are realized.

NY is a good example of how this works--the first wave of exits, the ones that purported to show a close race, were overrepresented of Buffalo, NY--Bernie's best metro area in the state (and where I live). The reason for that is practical, Erie Country was one of the very few counties outside of NYC that opened polls in the morning instead of at noon. So it got hit with a lot of exit poll takers, again, for the first, early wave.

There is no exit poll conspiracy, none.