It's far more complicated than what I'm about to write here, but...

It's far more complicated than what I'm about to write here, but overall the shift in sentiment is due to many factors such as uncertainty in the global outlook, the tightening of monetary policy, the slowing of growth, the recent trade war talk from Trump (additional 200b of China goods to 25% from 10%), brexit, the Fed's chairman Jerome Powell's speech on Wednesday and in particular the general distrust of and pessimism towards the FAANGs. Now throw in rumours of regulations, anti-trust laws along with nebulous guidance (see Apple etc) and the whole sector has grown sour and incalculable. Then add on top of that how useless most Australian investors are with their lack of foresight and you have something approaching an answer.

My 2c anyway, though very happy for others to enlighten me too.