Thats true, having a license doesnt guarantee that the casino is not scam and can be trusted in the long run because this still depends on the casino's build reputation and it really takes time. Roobet is one of the trusted casino existing nowadays and I bet we are aware of their reputation here and outside. They're consistent with their marketing strategy and promotions and if there's an issue they are fast to resolve it. Plus their support is online often if there's an issues which I like the most.
I have no idea about license of gambling but there are a lot of business who opens their busienss first and then try to take licence and also on several business licence cant not be approved for several months/years but it doesn't affect too much on their business. It may happen for gambling too.
There are renewal charges and having an license is costly task and there are lot of other implications that needs to be fulfilled but most of the casino first of all go for license as players search for the details before joining any casino like us.So at this time Curacao license is the most famous and somewhat cheap at this time so you will find most of the casino operating under the same license.But after that they can turn out to be scam also so make sure you play over legit casinos only.