Why do humans choose to deny the despair right in front of them rather than face it?

That's how they were raised - either by examples or someone was always there to shield them from the discomfort of life - constant bail out. They're just not equipped to handle issues.

What good does surrendering to despair ever do? Fight it! Deny its power! Take the high road and allow hope to support you through the worst that life can inflict on you. It's stupid to just roll over and die without a fight.

they do? i was not aware this was the case, since i face my problems head on.

Yes some do, they feel they have no way to change their situations, see know way out of their problems, or become overwhelmed and cant do anything from their depression.

We all have roles to play in the lives of others. Realizing this would help bring about more activity that would benefit others, but if a person does NOT realize it, then it is possible they were never taught about it. That makes it not their fault.

If the awareness is there, they still have a choice, by simply being born. It's free will. Some were not born with this capacity. Others feel their plates are so full that putting one more thing on it would make everything come crashing down around thier ears. Still others do not have time to devote to it, literally.

There are a lot of valid reasons why a person won't help, or can't help. Before we assume that everyone is cold and heartless, we must first look at WHY they aren't helping. +5

Which despair is that?

Despair is an emotion that comes and goes, and is very subjective. Your question sounds a bit like you think it's floating out in the universe waiting to land on people, like a cloud of mustard gas.

In general, though, we don't like negative/threatening emotions, and are pretty good about suppressing them. As you've hinted, it's better to experience them squarely.