That is because exchanges require it as a must, whereas most casinos including duelbits require it when needed, plus exchanges like binance has like a trillion users lol, duelbits doesn't have that many users and don't need that much quick work on it right away. Which means that they could manually check every single case and they can make a decision that way as well.
I feel like there is going to be some sort of situation where it's not even happening at most given times. Like there could be weeks where they do not need to check any KYC at all, why would they want to work with some place or even hire someone specially for this when it's not needed that much.
If I am not mistaken and I could be wrong, you didn't need to pass KYC on Binance to make use of it (years ago) but since then everything has changed. I know this topic has been discussed already a lot, but more and more casinos are requiring KYC so probably Duelbits is checking this daily.
You are talking about when it was early days but now using exchanges doesn't grant you any sort of privacy like Binance have strict KYC regulations.To follow the rules and regulations casinos also have to comply with these norms and this has been issue of the past but now many have adjusted with it.