There's one weird trick Blizzard / Netease used to avoid (some of) these laws. A game system that gets classified as gambling usually does the following:

User pays money > User gets premium currency > User presses button > User gets random reward(s)

Here's DI's version:

User pays money > User gets premium currency > User "uses" item before rift > User plays rift > User gets random reward(s)

That extra step means that instead of simply playing a slot machine with real money, you're playing a (very very easy) game segment that gives you (exponentially better) rewards, since you used real money.

Most anti-gambling laws require the digital goods to be exchangeable for money in order to qualify. In other words, DI can claim to not be gambling because all outcomes in the rift are equally worthless, financially.

Some countries are starting to change their laws to factor in that these digital prizes are perceived to be valuable by players despite not turning into money.

The game is banned in the Netherlands and Belgium.