To answer your question, I think such a game cannot be installed in most casinos due to laws. But there are countries in which they could exist in casinos, I am sure. But they can definitely find a crowd in online casinos. But then again, that would just be Pokemon. Maybe that's the reason casinos do not include this in their gambling games?
As i've said in my previous post above that in our country there is this online cockbetting where you can bet anytime, anywhere as long as you have an internet connection and it used to be legalized by the government but now it stopped due to some complaints but you can still find online cockbetting but not that open anymore as it is already illegally operated. Online cockbetting could generate billions of pesos that i think it is a bigger platform that a casino in our country which is why it is very hard to stop/eliminate.
But the biggest reason is probably that its hard to make a skill-based game into something luck based.
Cockfighting is more of a luck-based game though your bird has a high chance of winning if it is well-trained but in the end luck should be on your side most of the time to win.