I am to provide some context, in many of those countries people do not normally fill in tax reports, themselves, either. Lots of those countries have rather sophisticated regulations when it comes to gambling.
Take Italy which (along the UK) has one of the largest gambling market and the strictest regulations. Effectively every bet is sent to the regulator in near real time and some stuff like bringing money to the table (game) requires an explicit approval of the regular beforehand. To put it simply taxing the gambling firms, that already need a license, is much easier.
There are monthly reports, regulator mandated vaults that have to reflect the state of each player, including all bets and wins done, player (and operator) set limits (e.g deposit limits)
So overall not taxing the end user is a good choice, it just it's a lot more involved that just 'no taxation'
Take Italy which (along the UK) has one of the largest gambling market and the strictest regulations. Effectively every bet is sent to the regulator in near real time and some stuff like bringing money to the table (game) requires an explicit approval of the regular beforehand. To put it simply taxing the gambling firms, that already need a license, is much easier.
There are monthly reports, regulator mandated vaults that have to reflect the state of each player, including all bets and wins done, player (and operator) set limits (e.g deposit limits)
So overall not taxing the end user is a good choice, it just it's a lot more involved that just 'no taxation'