In between investing in BTC or real life casinos, I think is while better to do it online, since we cannot know if the site itself is not scamming by having algorithms to make people lose.
Also, it's affordable to invest online and there is no legal requirement just to investment, in overall it gives convenience to small and big investors. The market is wide, because most gamblers will prefer to just sit in their chair and gamble at home, I think it's the trend now and it has continued it's popularity.