An old tradition which also been legalized from some places in a small third world country, it's hard to remove that old culture where the enjoyment has been part of this kind of gambling.
I understand the point about animal cruelty but for those who are engaged in this culture
they only understand what they've believed. It's tough for them to change as they will continue
to participate and keep betting on this kind of gambling.
It seems to me that there is no need to prohibit such entertainments and to ensure that they die out by force. Culture is inevitably changing (and it has been happening at a rapid pace in recent decades) so these forms of entertainment will naturally become a thing of the past. As far as I know, bullfighting was banned in Spain after, in fact, public interest in it had fallen sharply. When cockfighting becomes not part of the culture but a marginalized entertainment, then it will be relevant to completely ban it.