I think that's one of the most common reasons for sure.
But some of them develop that fear because they fixate on one girl for a long time, crushing for weeks, months, sometimes years.
Then after just a few rejections like that, it's understandable why they get all discouraged. Their whole approach is bound to even very desirable men lose hope.
It's easy to fear rejection if you fixate on a girl a long time and start caring about her before even asking her out. It's so much easier to ask a girl out when the feeling is not much stronger than for any other pretty girl out there.
It makes sense, but I don't think it's truth 100% of the times. Well, there can always be a really unlucky guy who got rejected by every girl he asked out and he never had any girl asking him out, it's possible.
However, in most cases, I agree with you. People who fear rejection are much less likely to make a move and won't date anyone as a consequence.
Well, I have never dated before and I've tried many times. Every single one of the women rejected me. The ones that did hit on me though were all the ones that I am not attracted to, as in African Americans.