Imagine you're a D&D player, you like your RPG's hard and with high stakes, no resurrections, rolling for stats, a different class/build every time to keep it fresh, maybe even some homebrew like no healing potions, only a certain amount of PC's/allies per dungeon/boss, stuff like that. But the most important thing to you is the roleplay aspect, building a personality around your character, constructing a fun narrative around the party and getting genuinely invested in them which makes it sadder when they die.
Now imagine one day some guy calls himself the best D&D player in the world. He plays the game differently, he runs "hardcore" campaigns with deliberately over tweaked encounters that are designed to kill you over and over again, and everytime they do you start from the beginning until you've got 30-50+ attempts on the same campaign. He plays with the Dungeon Master's guide and Monster Manual open at all time instead of relying off memory, he'll calculate encounters before hand, attack/damage rolls, averages, probabilities, ect, but its okay, these campaigns are so hard you pretty much have to, right? He runs the same overpowered Twilight Cleric/Moon Druid/Hexblade Warlock builds every time, rerolling until he gets an optimal stat spread, apart of the same optimal party composition every time. And lastly, no roleplaying, they're just RPG characters they should be played optimally, they don't need personalities or gimmicks, also no side quests or encounter grinds to get to a certain powerlevel, they just auto-level to the next encounter level cap, I mean it saves time, why wouldn't you?
The influx of new fans agree this is the preferred way to play and generally conform to their ideals, while the old guard of roleplayers disappear and are replaced by powergamers.
This is the current state of Nuzlockes