The first is, because of the creation of special effects, and before the movie was released the cast would do a pre-screening of the film they were making. Once special effects became a thing the pre-screening of the film wouldn't show the film properly because the special effects were not in yet. and this could have made it harder to make a film with an Auteur director.
The second reason that the Auteur director could have come to an end is that, after Star Wars was noted to be a huge hit, Directors started to push out these B movies faster and as this documentary notes, "it almost didn't matter if they were good or not." Furthermore, because they were pushing out these B movies so quickly directors started to only care about the money. lastly, this is a definite reason the rein of the Auteur director could have come to an end, and it did by the end of