The reason is simple: Consider Market Capitalization and you will understand why Ripple is one of the best to have at both Primedice and Stake

With future growth of Ripple, Ripple investors will feel much happy and use part of their coins to bet on casinos, includes PrimeDice and Stake.com. There were some flippenings between Ethereum and Ripple in the second and third positions on coinmarketcap.com in the past. It is obviously that Ripple is a very very strong altcoin