Why would they? Isn't it impossible to beat blackjack in a long run with 6 decks and such?
What's that old line..."The markets can remain irrational longer than you can remain solvent."
Similarly, even though a player may lose asymptotically to the house, they can be quite annoying in the short run.
Not impossible, but you do have to do some brazen, easily-detected stuff like watch the table for awhile and refuse to sit down unless the count goes positive.