Not because there is no law, it simply means legal. Remember there is also no law that states that online crypto casino is legal. Remember when we use the term legal, it is permitted by the law, but in this case, there is no law that define the legality of the said online crypto gambling.
I find this very confusing- it does not necessary mean that a law must be published in order for something to be legal.
Though this may be an extensive topic and discussion, I humbly submit that an act, for it to be considered illegal, must be written down on some sort of mandatory law. We live in a world where laws are more of "prohibitory" rather than "mandatory" only with a couple of exceptions. By applying such, I do think that if there is NO law expressly mandating gambling activities to be illegal, then it is legal perse.
It is going to be a difficult situation if an act, which is not expressly prohibited, suddenly becomes illegal after the consummation of such activity. That would amount to an
ex post facto law[/i] which is definitely unconstitutional.
Well with all things considered, I still humbly submit that there must be a law expressly prohibiting a specific act for it to become illegal. The absence of such law means that it is indeed, legal in all aspects (though there are exceptional circumstances and examples here).