There are quite a lot of gambling sites or online casinos that have the same UI and other features, this does not violate copyright, in fact, competition will get tougher and each gambling site will try hard to provide the best service to their users. i also saw gambling sites that are owned by just a group of companies but they have many names of gambling sites and monopolies like this are actually what makes new gambling sites appear with little chance of making it big in the gambling market. just like you, i will only choose gambling sites that make me comfortable both in terms of security and fast response.
I will add that even if the web designer of a casino wanted to be as original as they could be when it comes to the implementation of their UI, there are also limits they need to adhere to, so it is not like they can do whatever they want with the UI.
And once they take some choices about the design of the casino they will find themselves limited, not because they do not have good skills, but because of the expectations of their own customers, as if the UI is not intuitive and they need to look for everything since the UI is too different compared to what other casinos have implemented, those gamblers could simply leave and go back to the casinos they already know very well.