Pretty much this. It's common advice, especially for young men, to go out there and get rejected as much as possible.... but the ugly truth is that not everyone has that kind-of fortitude and moreover not everyone gets the same level of rejection.

This is going to do a tapdance on the line between sounding defeatist and making a valid point, so hear me out.

Some people really are just socially acceptable enough that they can weather dozens to thousands of rejections because a lot of the rejections just aren't that nasty to them, and/or they aren't as rejected in other spheres of their lives. Maybe they have a decent job they get along ok in, or are doing adequately in school. Maybe their home life is actually pretty decent, or they have a solid retinue of friends. Maybe they have a much more conventionally attractive face/physique/fashion sense than they give themselves credit for, which really does lead to overall nicer treatment from the world.

A lot of people don't have those kinds of safety nets to fall back on. When you're not doing well there are a lot of societal reinforcers to remind you of that fact, and as a person ages you're reminded constantly of what has already passed you by. After a point you really do start to wonder "is this just my lot in life?"

Now it's not hopeless, both technically and actually, but it's not hard to see how things can create a compound effect that a lot of people find too hard to resist.