They can start their business with their platform structure, attach games from partners and move on. Building own games has risk too and it can affect their business income, security and more things.
BC.Game are not a brandnew casino and their existence in this gambling industry is long enough. They have many things achieved through their long existence and operations like reputation, customer base, security and experience in Business Development.
All these factors are helpful for them to decide what to do with budget for marketing to minimize money wasted to ineffective marketing types and with their recent marketing propaganda, I agree with you that BC.Game is on fire. Their business is scaling up successfully and the bull market will help them to do it more effectively in several coming months.