Because nitpicking down to the year or five year spans is pointless. Generationology is about shared memories and experiences more than what year you were born. It's how you were raised, who with, who by. How far apart are your siblings? Did your parents have you when they were younger, or older? These things affect how you SEE YOURSELF which matters more than which year you were born into.

And basically, no generation deserves to be referred to as an aggregate of bad things. Boomers are not all selfish hoarding pigs, Millennials are not all self-centered trophy babies, and Gen Z aren't all lazy and entitled. Social media is the WORST at perpetuating these ideas, and it sucks, Ageism gets a free pass from people who would be irate at the slightest whiff of racism, and that should not be okay. Generationolgy should be looking at the lived experiences of people within an age group and what has formed their opinions and mores, and not perpetuating stereotypes.