What is a reason someone might risk it all to rob a bank?

Desperation!!!

Their son or daughter's health.

To save my son's life

because what they are risking isnt worth having. that and theyre stupid. id like to see a % of how many bank heist actually succeed. i know it does happen on occasion. but id like to see a success rate.

When you are in debt up to your eyes.{invis points

If in desperation and all other avenues have been taken to save a loved one's life and health.

Extreme desperation and limited brain power. I would rather be poor than in prison.

You know, if all our pensions disappear in the next 20 years, robbing a bank may be the only way to get 3 squares a day, shelter, and clothes on our back. A prison designed especially for "seniors gone bad".

To pay the power bill, the mortgage company, etc. My Brother-in-Law is an investigator. He says the crooks get away with it a lot more often than when it is publicized. The successs rate is never publicized because it is believed that it would inspire more to do the same.

We must take into account the fact that many people don't have the skills needed to get a good well paid job.
In the end they are surrounded, by what may appear to be hundreds of people who have it all.
So sooner or later they decide to just crab what they can, most start by doing a few petty thefts and soon they want more and more until one day they walk into a bank with a gun and BINGO!
The chances of robbing a bank and getting away with the cash is very remote indeed, but the people that do it lack the brain power to process things like that.
I have in the past had to treat people with addictions.
Like a twenty year old girl who's IQ was below 70. So had been charged with many petty crimes and in the end started to do more and more, to pay for the drugs she was on. After living on the streets for a few months she ended up being HIV positive, with a number of minor infections which finally killed her!
Her funeral was attended by nobody at all and she ended up in an unmarked grave on public land.
Her worst crime was her lack of life skills..

They worship money. It doesn't matter if they are motivated by love or fear, they worship the power money has to improve their current situation. So much so, they make a stupid choice.

Actually most bank robberies are pretty supid in that the tellers have limited amounts of money and some of it is marked (in one of several ways) or numbered.

to protect the people they love

They're broke.