There are a bunch of desperate guys out that are always on the lookout for the perfect girl that will be theirs forever. Although all the time that is not working out for them. Why are these guys being rejected by girls that are coming and going. Why are women rejecting them?

You're probably going to have to expand on this a little more. I cannot figure out what it is that you're looking for here.

Why are women rejecting them?

They don't like them, have time for them, have other things on their mind, have other options. The reasons are endless.

There are many guys out there that think that because they're looking for a girl, want to be with a girl, that every girl they meet should be thrilled to death to be getting their attention. The fact that you said that these guys are desperate, says it all. Desperation is a huge turn off to women. A woman likes a man that's confident, not a man that's so desperate he'll hit on anything with a pulse, and that's not even the main criteria!

Stop the desperation, realize that just because you want someone, doesn't mean they have to want you, gain some confidence, and stop hitting on every girl you meet, and you may get somewhere.

Because they are desperate and come across as such. We don't want desperate men. We want confident men.

Men don't like desperate women, clingy, needy, whiny, eager for that engagement ring, demanding of time, jealous and possessive - right?
Women don't like men for the same reasons in different ways. And they certainly don't like men who think they are perfect just because they are looking for the perfect woman.
Perfect woman? No such thing. Just as there is no perfect man.

Men need a life. That means interests and skills and talents and knowledge and opinions and thoughts. Women do too. Too many of both think they are not anything until they find someone. The actuality is that 'having a life' is attractive. Look at all the people who meet someone in a course, or outdoorsy group, or their career, or volunteering, rather than hanging around some bar or park trying to look handsome/beautiful.

Did someone reject you? If yes then don't think about it. Don't be desperate and women like friendly and honest guys.