If all people did that, nothing new would get done ever. It's a risk. Developers who embark on wheel-creation know it's a risk. Nevertheless, rejection still hurts. Being ignored doesn't just mean you invested all those hours for nothing, it also means the audience rejects your take on the subject, and by extension your value system.
But telling people to just stick to established open source projects and be content with small contributions is not the solution either: first this would probably not be an interesting activity for those people and second participating in a successful OS project is by no means a protection from this kind of rejection or other kinds of grief. The "solution" here is clearly to "suck it up and move on", but I see how that can be difficult.
I'm afraid the only real advice to give here would be for developers not to get too invested in their pet projects because, like startups, most of them will never be of any interest to anyone. To all the people who are currently doing such projects, I'd say: keep doing it as long as it's fun, but not a second longer. Learn to let go.
This person clearly went on beyond that point.