Is it really so clear? Anyone who thinks AAPL is overvalued (including you) can make lots of money by shorting or using puts appropriately. People aren't doing that, so they must not be very confident about Apple's stock price decreasing.
It costs money to keep short positions open - there are several examples of people who exited short positions in the subprime-mortgage bond market just before the credit crunch. They were convinced that the market was going to crash, but they didn't know exactly when.
I said it depends on Apple doing something wrong and I can't predict when that'll happen or what it'll be but here are some suggestions: Making the iPhone 7 out of cheese or Tim Cook farting in the wrong direction. Either way, if the markets have shown us anything in the past, it doesn't take much at the moment to send traders into sellmageddon mode.