Why most of the people ignore mental illness?

Most of the time it's not ignoring. It's unconscious displacement. People don't want to think about things so they mentally block them out from feeling uncomfortable. We do it all the time. It's a psychological survival technique. Keeps us from thinking about dying babies or possible office shootings or car crashes. Don't assume people are ignorant please. Human body does what it needs to survive.

People don't always understand it cause they don't deal themselves or someone who has it. So they don't handle well or know how to handle it at all.

Because it is easy to ignore, very few signs unless the person suffering says something or you care enough about the person suffering to notice there is a problem.

Because there always has been a stigma associated with it. One day, hopefully it will only be a "illness".

They're ignorant about them.

How would you define mental illness? Is it something you would never do, is that enough? Who decides if it is mental illness? Maybe the diagnosis is wrong.

cuz people do not want to waste their time with them. Unless they can make(steal) money from them. Then they will give them some attention.

They don't know what to do, and the stigma that mental illness is a flaw.

I don't think most ignore I think most are afraid so they hide from it