In the case of Diablo Immortal, this is the method of using Legendary Crests (which can be obtained or bought) to increase the chances of a gem that has a 5-star rating appearing in the dungeons at the end of the game. Although it's not exactly conventional in its presentation (most gacha are performed by "rolling" on a short-lived banner) Players are engaged in the same kind of D2R Items randomness that they are used to in other games in the same manner. In many ways in many ways, gamers are using the Diablo brand has been building towards these mechanisms since it's inception, in the words of Maddy Myers wrote a few weeks in the past.
Diablo Immortal also, in the simplest terms, takes direct inspiration from a "feeding" mechanism that many Japanese, Korean, and Chinese mobile games have adopted for over 10 years. "Feeding" involves raising the stats, attributes, or rarity of an item , by creating duplicates of an item drop. These duplicates are then fed to an item with the same rarity , thereby increasing the overall stats of an item. In general five copies are needed as industry standard to max the character or item.
My first exposure to "feeding" was through Fate/Grand Order, which was initially published in Japan in July 2015 and brought in a total of $4 billion dollars worldwide in the year 2019. To make a character as good as it could absolutely be, I needed to obtain copies of each. If a certain announcement came up I spent upward of 300 euros to acquire the 5-star character I'd been lusting over all my life. However, I never obtained the exact copies I required for the full potential of this character. The rates for the top five-star characters hovering around 1%, so it was no surprise I never managed to acquire a copy of the character in my time using the game (which I've since uninstalled). As of the end of July 2021, Fate/Grand Order was the seventh highest-grossing mobile game of the past, and was placed behind Konami's Puzzle and Dragons. It also, I'm guessing, is also a gacha-based game.
During a GDC 2021 speech, Genshin Impact developer Hoyoverse (previously Mihoyo) outright admitted that the method used to create characters revolved around generating the maximum amount of capital from its fans. In the case of Raiden Shogun and Kokomi characters that were reruns in March 2022 alone netted the company over $33 million in revenue.
The event was immortalized in humor and memes, the bulk of which stemmed from low expectations from the crowd: People attending BlizzCon 2018 were expecting "Diablo 2 Resurrected" announcements. But the reason for this was an unease about gaming on mobile devices in the West as the adoption of smartphones as a gaming platform is slower than in the Diablo II Resurrected Ladder Items rest in the rest of the world.