Real-money transactions aren't novel by any stretch of imagination. Diablo 2 Resurrected didn't pioneer them, and it would be insincere to make that claim as the case. Blizzard's action RPG isn't the main source, but it is instead the D2R Items worst amalgamation of hundreds of free to play mobile and PC games. It comes with two distinct Battle Passes, each with specific rewards that are specific to the character (and not to your entire roster) and with too many different currencies for the average player to keep track of, Diablo 2 Resurrected's economy reads like a gigantic mobile marketplace.
These practices, though sometimes opposed however, have become commonplace within the gaming industry in general. It is possible to argue that the prevalence of loot boxes or other real-money transactions within AAA games has contributed to this kind of predatory economy -- but the more AAA gaming shifts to the model of games-as-a-service more, the more it has to do with portable games which have existed in this wildly popular field for over a decade.
It's not just evident in the use of paid currency to obtain items as well as gacha mechanics, as well as the publication of drop rates of more rare items. Gacha is the practice of making use of in-game currency, regardless of whether it's free or acquired from an in-game shop to buy something random like pieces of equipment for instance, in the case of Dissidia Final Fantasy Opera Omnia, or characters in the ever popular (and constant) Fate/Grand Order or Genshin Impact.
In the case of Diablo 2 Resurrected, there's the usage of legendary crests (which can be purchased or earned) in order to increase the probability of a five-star gem showing up in the dungeons of the endgame. While it's not completely traditional in its presentation (most gachas involve "rolling" using a time-limited banner), players are still engaging with the kind of randomness in the same way. In many ways in many ways, the Diablo franchise has been working towards these types of mechanics from its beginning like Maddy Myers wrote a few weeks back.
Diablo 2 Resurrected also, in clear terms, draws directly from an "feeding" gameplay mechanic Japanese, Korean, and Chinese mobile games have been utilizing for more than 10 years. "Feeding" entails raising the stats, attributes or the rarity of an item by Diablo II Resurrected Ladder Items making duplicates of a drop. The duplicates are then fed to an item with similar rarity, which increases the overall stats for the item. Generally, five copies are required as industry standard to max out a character or item.