I think Primedice should change their jackpot winning system. This isn't so easy to roll 77.77 twice. There is some min bet limit. Moreover, the system isn't automated. User needs to contact the support team if he/she is eligible (meet the requirements) for the jackpot.
Changing the manual system into automatic system is more than enough to make it more attractive.
Basically not many dice players are focusing on the rolled number while they are playing as most of them are focusing on the result only (win or lose) unless someone is hunting for the jackpot or hunting specific number for contest.
Other suggestion from me related to the jackpot is that lowering the min bet or at least give small rewards to players who hit 77.77 twice in a row if their bet amount is below the current min bet requirement for the jackpot.