Casino bonuses are only generally offered to players from certain countries.
Some casinos only list the restricted countries in the Bonus Terms and Conditions (T&Cs) for each specific bonus, claiming that their system is not able to ensure that only players from eligible countries get the bonus. This is extremely unfair towards players for reasons similar to those listed in the restricted countries situation.
If these restrictions are not technologically enforced by the casino, players may receive a bonus they should not have received, only to find out about the restrictions when the casino declines to withdraw their winnings. If a player can claim a casino bonus, they obviously assume that they can play with it and don't have any reason to think they shouldn't have received the bonus in the first place.
Casinos should be equipped to only give out bonuses to eligible players. If the casino is not equipped, it should let players withdraw their winnings even if they are from a country that is restricted for bonuses. In other words, once a player gets a bonus, a casino shouldn't take it away from them or confiscate any winnings that originated from that bonus (unless some other rules have been broken).
This issue often starts with the marketing. Casinos or their affiliates often send emails about new bonus offers, sometimes to players who are not eligible to receive them. Players then have every reason to believe that bonuses are available to them, which may not be the case according to the bonus T&Cs. Therefore, this information should only be sent to players who are eligible to get the bonuses.
A fair casino should only give bonuses to players who are allowed to get them according to the Bonus T&Cs. And if the casino makes the mistake of granting a bonus to a player who shouldn't have received it, the casino shouldn't take it away from them. Instead, the casino should accept that it was their mistake and pay out the winnings to the player.