At the time, The New York Times called the 2010 creation of what became known as The Giving Pledge, “The biggest event in philanthropy this year…a commitment by 40 of the wealthiest Americans to give away at least half of their fortunes, about $600 billion.”

Started by Bill Gates, along with his then-wife Melinda French Gates and Warren Buffett, more wealthy people continue to sign on every year. As an Institute for Policy Studies (IPS) report entitled The Giving Pledge at 15 details, the initial group of 40 people quickly increased to 57 by the end of 2010.

Today, a total of 256 individuals, couples, and families have signed the pledge, of whom 194 are from the United States and 110 are US-based billionaires. This means that more than an eighth of the 876 billionaires in the United States—with a combined wealth of $1.7 trillion—have agreed to give away at least half their fortunes by the time of their death.

Sadly, however, the results have been disappointing, especially when compared to what their large wealth holdings would suggest. According to the report’s authors Chuck Collins, Bella DeVaan, Helen Flannery, and Dan Petegorsky, “giving pledger” gifts after 15 years total $206 billion—far shy of the $600 billion originally anticipated.

Of that $206 billion, about $164 billion went to foundations and $5 billion to donor-advised funds. As a result, only $37 billion has gone directly to nonprofits. Of course, grants to foundations do create or increase endowments that support annual giving. Even so, the results are, broadly speaking, less than inspiring.

What explains this? In their report, Collins and his coauthors break down some of the challenges. These include the slippery nature of the pledge itself and the ongoing impact of a society and economy that favors an ever-increasing concentration of wealth.

You Can’t Cheat Death, But You Can Cheat the Pledge

The home page of The Giving Pledge states: “The Giving Pledge is a promise by the world’s wealthiest philanthropists to give the majority of their wealth to charitable causes in their lifetime or wills.”

The pledge, of course, is voluntary. But another challenge is that pledge fulfillment is set far in the future—after death. Even if the pledges were not fully voluntary, enforcement after death would be exceedingly difficult.

Read the full article about The Giving Pledge by Steve Dubb at Nonprofit Quarterly.