4chan

This here is the answer. Unless you're scouting a table for a long while, you generally won't know how many in the shoe. That, mixed with the fact that mentally keeping track of 250-500 individual cards, not only is near impossible without an aid; you would also only have so many opportunities to "know" what cards are left. Thus, the 30 cameras pointed at you and identifying that you've been playing the same table for hours, they're going to know.

In reality, the casino industries current weak point is their electronics, specifically the slots. The software running on those things has been proven to be about as vulnerable as a payphone, and people have been caught running schemes on them.