Some posts here are not exactly necessary if people bother to read the information given by OP on the opening post and the supplementing post given by others.

OP accessed from Australia, it's one of the restricted territory. Accessing Rollbit from this country warrants account termination and/or fund confiscation as per agreed by OP on clause 6.1., restricted territory; explained on post #2 with a screenshot of the said ToS shown on post #3 to make things easier.

Where does Rollbit knows OP play from Australia? It's by OP's own admission, provided through his chat log on the opening post,



And OP, your question, "If they can early detect countries they don't want players from, then why allow do they allow them to even play?", well, they don't.

I try to replicate your situation, by accessing "from" AUS, the result was as below,



Note the timestamp I mark in red underline, to show that I indeed accessed both pages within the same time, that I'm still effectively in AU through VPN [proven by the result of whatismyip. You should get that pop-up I pointed in blue arrow. So the only reason they "allow" you to do so, I dare to assume, is because you click that small x button on the pop-up message and disregard the warning.