It is possible for one to open up a casino without a license and I think it can be considered as legal not unlike to some serious business outside that if you don't have a license your business will be tagged as illegal and you will be in great danger once some inspect you.

For some users, it might be true that it gains them a confidence while for the rest, they prefer casinos with no license because a no license casino usually don't come up with a KYC requirements. I think there are licensed casinos on the past who still turned into a scam later on, and there are no license casino who continues to stay's legit so being trustworthy it's not about the licenses.