Adding all that coins is not necessary when there arent really large demand on it. First of all, Roobet is not the site that is fond of micro betting. Roobet has withdrawal limit of minimum $10 and this is merely to discourage people to deposit small amount . So most likely players are going to deposit over $10 on the site and paying $1-$2 transaction fee isnt really a biggie for those players.

Doubt that Roobet is going to add doge or any other coins for the sake of cheaper transaction fee. If anythings were going to be added in the future, it will only because those coins are popular

Plus the majority of their players isnt on bitcointalk , also they dont really have any complaint about adding new coins or transaction fees so yeah this is not going to happen in the near future  

A lot of the crypto casinos are fishing in the same lake, so why would Roobet not add these altcoins such as doge, trx, ltc ? It can only attract more players. Majority of their players is indeed not on bitcointalk, but maybe they get these requests every day...
Personally, I am hesitant to pay a 1-2$ fee on small deposits, that is why I would prefer to use doge or trx.

Anyways, it was only 0.15$

Lucky me, I just turned these $0.15 into $20.48