Maybe the just wanted out. Maybe the owners just wanted to move on to the next venture. The only people who know why the decided to shut down the business and sell it are the owners. Do you have any evidence to back your claim that it's a failed business?
If New owners came up with new good marketing strategies. Do you think they can't make any money out of BetBTC?
I don't know how profitable a crypto business is, but selling it for less than half a million dollars, I think it's fair enough since they build their name for many years and they maintain their good reputation. Probably if the new owner will go for a more aggressive marketing strategy, they can make this site to be more profitable, and in just a few months or years, that ROI will be achieved.