High amount of RNG is mostly a tradition of American tabletop game industry that had been carried to early video game industry. Tabletop games from other places may use less RNG, there is a more deterministic class of tabletop games called Eurogame, for instance. Just because many old-school hardcore RPGs (that have been influenced by American tabletop games such as D&D) use a lot of RNG, doesn't mean there is anything inherently hardcore about it.