I only use Bitcoin and the occasional dogecoin as a coin if I want make a deposit so I don't feel the need to see the casino where I play adding another coin
Casinos want variety for payment system so that their games will be easily patronised and so they add dogecoin because of the fees that is very good for gamblers. Not every gambler have bitcoin because some trade dogecoin and transfer same to gambling account to play. So it is still in use as option for some gamblers.