8 decks are shuffled before every hand.  ==> That's what prevents people from counting.  It's the same as a continuous card shuffler used at many casinos.

When cards are dealt from a shoe, its possible to count (even with 8 decks, or 1000 decks), you just start at 0, for a low card 2-6 you subtract 1, for a high card 10-A you add 1, for 7,8,9 you do nothing.  When the count is high, there are a lot of 10's due up.  To defeat this, casinos use continuous card shufflers, ie they shuffle all their decks before each hand.  My website does the same thing.