online cockfighting is legal in several countries and so you can easily find it over the net. and still raking billions of dollars. and it seems that PH is leading on this one. then india, indonesia cuba, or france.
one can check this article -
Countries With Legal Cock Fight Bets in the World just don't mind the gambling site they are recommending here. do your own search of the site.
the existence of this betting type seems to be more on the tradition of the area. how they evolved thru time and sustain this traditional gambling game.
As a local resident of PH, I think the masses in our country are more familiar with cock fighting rather than poker or at least in my area. There are at least 2 physical cockfighting arena in my city and it's neighboring city and there's no legal casino around. I live on a province in the Philippines and it is easier to find cockfighting arena than casino to be honest. Even my late grandfather raise cocks to fight in those arena! This is why I didn't get shocked when an online cockfighting casino rapidly grow in our country. I think cockfighting is a norm here.
It's basically business for platforms or service providers, they are always in the lookout for what's popular in a region so that they can offer that to the residents. Now the local betting shops or platforms know that people there love cockfighting and it is a very popular game among the masses that live in there, so they understand that if they offer bets for the cockfights, they can easily earn a lot of money from that because they obviously take some commission for the bets and lost bets are also kept by them.
You can barely find any platform offering the opportunity to place bets on an international level because the game is basically banned around the globe and it's only some countries where it's still allowed and it might not even be allowed but local authorities allow it and they don't get those arenas seized.