Most of the JBxs are produced by one-sided thinking
I think that most of these JBxs ("Just be x"s) are products of one-sided thinking. I'll explain it directly.
It's rare when only one (just "x" something) thing may provide you with the sufficient attractiveness (if you haven't something else). For example, if we're talking about JBR ("Just be rich") it's (almost every time) enough; it's almost impossible to see a single rich man (except those volces or standardcels among the rich people). But all those JBW ("Just be white"), JBB ("Just be black") and so on are usually myths (known as "copes" in the incelosphere). For example, if a white (or black, yellow) man is just white and lacks of other traits (good IQ, morality, job, looks, achievements, etc.) it's nearly impossible to find someone who will just like him because of his whiteness or blackness, or yellowness... Even females who do prefer whites (or blacks, etc.) still will search for something more (at least personality and/or looks... often -- material possessions, money...) You know very well that many of the the present females are pickier than those years, decades, centuries and epochs ago.
The same goes for "JBT" ("Just be tall"), "JBY" ("Just be young") and so on.
Some of these "JBx"s are, in fact, collective (i. e. they don't express only one quality like "whiteness" or "height"), for instance, "JBC" ("Just be Chad"/"Just be Chang"). A Chad (Chang, Tyrone, etc.) is an attractive person (he is not just white/just black/just yellow, he is not just tall, he is not just young, etc.) who is strong, tall, handsome, masculine, successful (at least in 1-2 areas), popular (at least in his school, company, work place, district, street...)
My advice is to be careful when you read something like "Just be x" or "Just do x" because usually just 1 thing or just 1 activity isn't enough. As many of the incels know, there are plenty of platitudes like "Just take a shower (and you'll find a girl-friend)." or "Just hit the gym (and you'll ascend)." which are basic and necessary but usually not enough if you use only them.