However, people still gamble for various reasons.
We can assume that the people who still gamble are not from the religion that prohibits it or if they are they are not very religious. In reality too, almost every religion is averse to gambling, Islam is the only one I know that expressly prohibits any form of riba which will include gambling and also investing in Bitcoin, but Christianity is not welcoming of gambling either or any other religion for that matter.
Gambling is forbidden in Quran. That is why you will see Muslim countries that are strict against gambling. But in Christianity, gambling is not forbidden in Bible. Although you can see Christian religious leaders forbidden it as they count it as a love for money which is the root of evil.
The reason was simple, religious people believed gambling is owned by devils. I don't know where you can find in the bible that states gambling is a sin
No where in the Bible that says gambling is a sin.
That's right gambling isn't a sin, but it ain't a righteous act either! Its a rather tabu subject in some religions such as Muslim mentioned above, but even in the christian church its definitely not like promoted to gamble. Its not talked about in church unless its part of the message at least as a Christian. I personally think that there are so many things that could be considered synonymous with gambling you can't get away from gambling in some sort of way of fashion!