This is not true. Besides continuous shuffler machines, most casinos have 6 or 8 deck games that have plenty of 'penetration' (card counter term for depth into the deck that the cut card is placed) to offer an edge if you properly card count. There's also a big game to be played where rubes think they can card count and instead lose tons of money attempting to do so.

The problem with card counting generally is that the casino has infinite money and never runs out, thereby they can sustain large expected value swings... whereas you need an enormous bankroll to handle those swings, assuming they don't throw you out before that happens.

The book "Bringing Down the House" by Ben Mezrich explains in layman's terms how card counting works for blackjack.

There's plenty of doubledeck blackjack with good penetration in Vegas, especially in high limits rooms. The problem nowadays is that the casinos are also counting, and the patterns are simple and easy to track with the tech we all have. Changing your bet even a couple times based on the count can have the pit boss getting a call to remove you.