A version of this article first appeared in CNBC’s Inside Wealth newsletter with Robert Frank, a weekly guide to the high-net-worth investor and consumer. Sign up to receive future editions, straight to your inbox.

In June 2010, Bill Gates, Melinda French Gates and Warren Buffett started what could be described as the world’s most ambitious fundraising drive. After promising to give away the vast majority of their wealth, the trio asked their ultra-wealthy peers to pledge at least half of their assets to charity during their lifetimes or in their estates.

In two months, the Giving Pledge garnered signatures from 40 of America’s richest families and individuals to sign up. That first batch of pledgers, including Michael Bloomberg and David Rockefeller, was announced 15 years ago this week.

In the years since, the Giving Pledge has lost steam when it comes to enrollment. By the end of 2010, 57 signatories representing an estimated 14% of America’s billionaires had made the nonbinding commitment, according to a recent report by the Institute for Policy Studies. Currently, the pledge has commitments from 256 individuals, couples and families, including 110 American billionaires, per the progressive think tank. This group makes up 12% of the U.S. billionaire population as estimated by Forbes.

The annual number of sign-ups has also flagged since that first year. Even in 2020 when the pandemic spurred wealthy donors to give more, the Giving Pledge only earned 12 new signatories. This past May, the pledge welcomed 11 new members, a marked improvement over 2024’s record low of four.

Meanwhile, over the past 10 years, the number of billionaires worldwide has increased by more than half to 2,891, according to UBS. Their wealth also doubled by more than half to an estimated $15.7 trillion, UBS said.

“It’s disappointing in that you would hope more people would step up,” said Chuck Collins, program director at the IPS and great-grandson of the meatpacker Oscar Mayer.

Collins, a co-author of the report, said the rapid increase in wealth may be partly to blame. This surge in wealth has also made it challenging for the pledgers to give away their money fast enough.

“Some of this is fairly sudden, the wealth growth,” he said, “so you got to give people … a decade of slack, if you just land in the billionaire class to figure it out.”

Whether the Giving Pledge has been successful depends on whom you ask. The IPS report described the Giving Pledge as “unfulfilled, unfulfillable, and not our ticket to a fairer, better future” and identified only one living couple to have fulfilled the pledge, John and Laura Arnold.

A spokesperson for the Giving Pledge described the IPS report as “misleading,” and said the IPS used incomplete data and excluded “significant forms of charitable giving,” including gifts to foundations.

“For fifteen years, the Giving Pledge has helped create new norms of generosity and grown into a connected and active global learning community,” a spokesperson wrote in a statement to Inside Wealth.

Collins said the Giving Pledge has some merit, describing it as a “community of peers among a group who don’t have a lot of peers.”

Amir Pasic, dean of the Indiana University Lilly Family School of Philanthropy, said it has had a lasting impact on how the wealthy think about their giving.

“I still think that it was really important attempt to socialize the new wealth that was emerging early on in this century,” he said. “We can interestingly debate how successful it has or hasn’t been, but it’s become a feature of the high-net-worth philanthropic landscape.”

Though Giving Pledge enrollment has stagnated, other efforts to accelerate giving have emerged, said Pasic, citing the collective Blue Meridian Partners.

And while some billionaires, particularly younger ones, may be reluctant to associate themselves with the Gateses and Buffett, it doesn’t mean they aren’t contributing in their own way, Pasic said.

“Buffett is the senior representative of new wealth at the beginning of this century. New representatives have emerged since then,” he said.

According to Collins, impact investing and other alternatives to traditional philanthropy have gained traction, especially among the new class of tech billionaires. He gave the example of Oracle‘s Larry Ellison amending his pledge to focus his resources on technology research instead of traditional nonprofit organizations.

“I think there’s a little more blurring between for profit and nonprofit, charity versus impact investing,” Collins said.

Venture capital billionaire Marc Andreessen has gone so far as to declare that innovating technology — and amassing personal riches in the process — is philanthropic in and of itself.

“Who gets more value from a new technology, the single company that makes it, or the millions or billions of people who use it to improve their lives? QED,” he wrote in 2023.

Pasic said it is possible that Bill Gates’ recent commitment to give away virtually all of his wealth over the next 20 years may bring new urgency to the Giving Pledge.

“I think that remains to be seen,” he said, “whether it’s going to end up being more of a kind of a private club that becomes less relevant or if it’ll be the beginning of something broader, gaining new energy in this turbulent time and or spawning other kinds of groups … or other collectives.”