Not only bustabit, but there are other platforms as well which have started with a single game and they continued their business with it. You can take Duckdice as an example as well which has been running with just a dice game and they added sportsbetting lately. I did not want to mention any names here. But, since they are not the competitor of Bitwinup, I don't think there will be problems.
Primedice could be another example which has been running for eleven years without any other games apart from Dice. How incredible their journey was. Even they have been hacked and the hacker stole 1 Million worth of Bitcoin back in 2014. But they are still operating their business.
Bustabit, Duckdice, and Primedice are just an example that it's possible for a platform to be a stand-alone, Bitwinup can possibly do that they are being managed by a reputable company and there's no other platform like them that is dedicated to Crypto trading arena.
It's the marketing that matters if they want to stay long in this industry, they have a good affiliate program and I'm sure they have other marketing stuff outside of this forum, they have established themselves maybe they will do a campaign here from time to time.