Philosophers, novelists, sociologists, anthropologists, and economists used to define, study, and critique generational divides before advertising became such a pervasive part of the modern economy
And they still do...
That eliminates the marketing effort to convince a consumer that they are part of a particular group. Getting individuals to self-identify themselves as members of various groups is a highly effective advertising delivery channel. Convincing you to use groupings as a convenient, time-saving shorthand (like branding is a convenient shortcut) gets you to buy more, more frequently.
Marketers and advertisers fear you insisting upon evaluating situations and people one-on-one, as they come up in your life, and using the marinating and revealing effects of time to judge value and character.