The house always wins is enough reason to never go near any casino

They can kick out anyone they want.

How is it allowed? It’s their casino. They’re there to make money off you, which is why everything stacks in their favor and any games involving any actual skill are hobbled severely and using any gets you banned.

Now if you ask “how are casinos allowed” I’ll ask right along with you. They are immoral and predatory - not literal fraud but it gets close, and either way it’s treating people with addiction as cash cows.

Generally speaking, a blackjack table will run with 5-10 decks in the shoe. So counting isn’t as effective, because the odds are diluted by volume.

Also, folks will often use aids to count cards, because keeping track in your head is difficult. What most people get thrown out for are carrying these aids.