I have different theories regarding the reason why casinos like to advertise on this forum.

Perhaps they think that anyone willing to invest into cryptocurrencies would be a person who is risky in nature and therefore would make a good gambling cash-cow? I think that might be correct, but only from a certain part of the community. A lot of us understand crypto is not gambling but rather it can be used for gambling. Those are two different things and they should be respected individually as such.

Or perhaps gambling was just one of the very first adopters of cryptocurrency and blockchain, and we as a community have therefore accepted it into our culture for this very reason?

It is really a bit hard to tell without extensive research.