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Another reason is cryptocurrency provides faster transactions and a level of privacy.
On their services, online casinos ask for KYC and actually the level of privacy is determined by this. Then crypto's built-in privacy is completely useless. It is no more convenient than conventional gambling for the privacy-seeking gambler, one can go to a physical casino and play a few games on fiat and leave like the wind.
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There are many more issues that I believe have hampered the churning of a traditional user to a crypto gambler. But the number one issue as per my research is individual preferences and circumstances.
Yes, especially regarding preferences, the use of crypto technically is still problematic for some age groups of gamblers. Or they don't even bother looking for alternative crypto gambling on the internet because they are comfortable with the current one.