A good reason there is a lot of work being done to separate the two offerings from each other. I'm supporting all sorts of features, but to pay, you gotta send Bitcoin with a client - not my site. Safest that way. Also, see Counterparty.

Edit: From the site in question: "Nowhere do we store or request any personal information." https://xbet.io/why_use_xbet

Another thing: It's not a forgone conclusion that Bitcoin technologies will get better over time, but there is a large amount of pressure to make that a reality. People like their money, above all.