I agree to that sentiment, casino owners will look for games that have possible good access in each country that they are offering their services, in terms of cockfighting, not so many countries are allowing this gamble so it affects the interest of online gambling casino owners, limited access means limited money to flow.
While with rural community where gambling into cockfighting is common, maybe chances for local casino owners to cater the game might be introduced, not sure if how they will provide or how they will attract gamblers to bet on it.
This is true because several countries limit betting options such as cockfighting which is considered too cruel to animals and it can also be seen that not many gamblers like cockfighting because only few countries are quite popular for betting like this.
For example horse racing is only popular in a few countries and only exists on certain sites and not all big gambling sites have betting options on horse racing.
But in rural groups bets like this are only done at small events and almost everyone has chicken that they want to bet on.
Although in some countries there are national matches which are held every few months for national level cockfighting matches.