Those countries that are allowing it probably are making a lot of money from it. They cannot ignore that there are many people hooked on it and that's why they just can't stop it wholly.
Not sure about the countries making money from it or not but the people involved are surely earning a lot of money, especially the event organizers who are taking bets from the audience before the matches.
If there are local authorities allowing this to happen and they're all good on it, then there is nothing people can do about it that are against it unless the organizations that I've mentioned will step in and will call for it to be stopped. That's what they can do if they're subject to it and whether there's gambling or not on it as long as it's exchanging fights and lives, they'll for sure going to take that into notice as that's their mission and advocacy.
Local authorities can also be bribed easily, we know that authorities in local areas are not that compliant when it comes to laws and orders of the country and they can always take some money and hide things that they are supposed to stop. Other organizations basically don't know if it is happening or not because the organizers obviously do it in discrete places if they come to know that the organizations are on the hunt for those who are organizing cockfights since it is prohibited.