Why is this game so buggy?

Don't get me wrong, I absolutely loved the game and it was one of the most fun experiences I've had in a while, even though it didn't scare me as much as I thought. But the one thing that made me curious is why are there so many bugs in it? I've seen AI bugs, audio bugs, graphic bugs etc. and lots of them too. They're not game breaking by any means, but they were definitely immersion breaking at times, why is it like that?