Beside the abusing of free dogecoin, they key issue is that it doesn't have those wagering bonuses and there is variable betsize (binded into DOGE/BTC price) as well as limited MAX win there, 800,000 DOGE by the last time visited the site. I once tried to write a dicing bot for it, but risk/reward ratio is not as expected (for the same strategy, a specified balance can't survive as long as if it is converted to BTC and played in the main site) as well as minimum bet size keep changing throughout the day (0.026 -> 0.03). If they are to make it interesting for gamblers and fixed the minimum betsize & max win, they can easily get out with profit regardless of abusers.
The issues with Doge are the amount of time it takes to fight abuse. It's a labour-intensive task and the profits didn't justify the costs. The other limiting factor is the Doge core software. It hasn't been maintained and updated as the Bitcoin core software has. That means that our node struggled to deal with the volume of transactions we were doing making it frequently lag the network causing support issues. If we had done anything to try and increase the volume on the site that would have just got worse.