Some people are fairly insecure and tie a lot of self worth to beating a hard game. The idea being that other people reaching the end of the game but having an easier time of doing it makes your accomplishment more hollow because they saw the same ending you did at a fraction of the effort. They see it as "unfair" because they didn't have to put in the same effort to learn the game as thoroughly. See the "You didn't learn" rant about Sekiro.

See also all the Souls elitists that decry using anything that isn't a "pure" build ie. Whatever they beat the game with. Obviously if you used mimic tear or sorcery or jump attacks, etc then you didn't learn the boss and beat the game the "right" way.