It is because bitcoin is the market mover and whatever things that happens to bitcoin affects altcoins.
I know that DCA is for bitcoin but I want to try the gambling but it seems that everyone is not in support of the move.
Bitcoin price influence most of altcoins, not all altcoins, it's mean even though halving will happen, the altcoins will not follow the bull trend.
If you want to DCA on other coins, it's better if you choose want you believe. If you ask someone to recommend a coin to DCA, many people will shill their own coin and they will promise a crazy return that will make you interested.
Gambling is better based on your own choice.