because it allows people to gamble from any location and with any device without having to use any identification or reveal themselves and all they need is a bitcoin wallet, in addition those websites are very dynamic concerning withdrawal and deposits.
This is the major reason why people are highly involved in gambling with bitcoin and other digital currencies because in this way they can fulfill their desires of making money with gambling without revealing their identities as compared to real world casinos.
Bitcoin provides you with high level of privacy which ultimately let you enjoy your luck and game without having fear of getting caught by family or friends.
I don't agree with you, i think major reason why bitcoin gambling is so popular is privacy, not only that you can hide that from your friend or family, but also that you don't need to provide any kind of ID card, usually you only have to register using email, which isn't that bad compared to ID card.