Because those that buy bitcoin when it is low at around 100-200$ already gain 5-10 times... meanwhile miners still trying to break-even 
I'll just say one thing. People who bought their mining equipment for BTCs did the most heavy mistake.
My friend put 90% of this BTCs to buy used mining equipment when BTC was at 100 usd. He got only around 40% of his cost in return (so far), despite operating the equipment almost continuously.