Yes, many players pay taxes only when playing in licensed legal casinos. In this case, such casinos act as tax agents. Casinos independently withhold income tax from the winnings of players (individuals). Thus, the taxpayer (individual) does not have to pay anything to the budget themselves (the casino should take care of this). This system seems reasonable to me.
They might act that way, but there’s usually a threshold, mostly for big wins. For smaller wins, it’s generally up to the players to report them. But here’s the catch, casinos still report those winnings too, so players really don’t have much choice but to declare, since it’s all on record anyway.