What is Online Gambling?

The difference is simple:
Gambling is when you put money in for a chance of getting more money out. Putting money in for a chance of winning prizes isn't illegal, which is why things like arcades and raffles aren't illegal in gambling-regulated areas.

You're citing two vastly different things.
One, an arcade gives out prizes as rewards for victors in Games of Skill. It's not gambling because it's not a game of chance, and the money paid in the skill contest is an entrance fee, not a wager.

Also, you're sorely mistaken regarding raffles. While in many states do not ban raffles outright, they are actually highly regulated.

Fine then.

Legally, virtual items don't fall under either legal definition of "value", due to a.) not being tangible objects and b.) not being able to be exchanged for currency under the ToS. That's also why they can't be taxed. The few instances of virtual item-related matters being taken to court were all settled before a ruling to the contrary could be made, from what I can find.

You can argue that it's morally wrong or whatever, but due to the way "value" is defined, it's not illegal until a court rules it is.

You're focusing too much on the "payout" aspect, and not enough on the wagers.
MapleStory itself is a free-to-play game. But contained inside of MapleStory are games that are closed-participation. They require a payment of real money to obtain a chance to win. That constitutes as "Consideration." Strike one. Gachapon and Miracle Cubes are literally pay-to-win elements situated in an enticing free-to-play game.

Gachapon and Miracle Cubes do not facilitate any user input, so the player cannot exercise any skill. Outcomes depend entirely on the fate of the random number generator. The game is purely Chance. Strike two.