Gambling is not legal in many countries.
This is the main reason people consider bitcoin or other similar currencies because you do not need to involve the bank to deposit the money and you will not get into trouble having a money trail to a gambling website and with crypto currencies you can easily deposit and withdraw without much fuzz and so is the reason people are opting for it but still we need to see a huge growth in the crypto based gambling websites as the fiat sites still rules this space.
That is right. People don't have to bother with the banks because they can do it by themselves. They can buy bitcoin or other coins to play gambling, and even they don't have to fill or to complete the account. Maybe this can make online gambling will get more popular in the future because people can find easiness in playing gambling without interfering with their bank's account. People will free to use their coins for anything they want, and they don't have to report it to the banks.