You're playing against other people, not against the casino. So, yes, some people will lose their money, but the more skillful players will win it.
You're playing against other people's bots, not against other people.
Not only do you have to program a winning strategy--which is very hard--but you have to not get caught--which is also very hard.
I know, I know: "if the operator is dishonest there are easier ways to cheat". But this looser collaboration between bot-operators and site-operators is easier to disguise, or to compartmentalize. It doesn't require dishonest software, for example.
It might even be easier for perpetrators to rationalize. ("These players are dumping their money anyway; it might as well be to my confederates' bots. Bot-training is a skill, too!")
You've got a distinct minority of people (I'd guess < 10%) who win the money from the stupid poker players. Since I am one of those stupid people I've decided not to pay the incomes of the advanced and more skillful poker players.
That doesn't include cash games, which probably has a lower win rate than 33%, but likely not as low as 10%.