Charitable giving by the biggest donors in the U.S. fell by 30% in 2015, according to The Chronicle of Philanthropy’s annual ranking of the 50 most generous individuals and couples.

All told, these donors gave $7 billion to their favorite causes, the lowest amount since 2010, and donations by technology sector philanthropists plummeted to $1.3 billion from the $5 billion they gave away in 2014.

The Chronicle uncovered several factors that may have contributed to the decline.

It said huge stock market swings may have caused some donors to hold off making megagifts, as both the Dow Jones and Standard and Poor’s indexes fell for the first time since 2008’s stock market collapse.

Another possible factor was what The Chronicle said were natural fluctuations of the list. In each of the past five years, a megagift has inflated the Philanthropy 50 total. In 2014, for example, two big donations amounted to nearly $3 billion.

Kathleen McCarthy, who heads the Center on Philanthropy and Civil Society at the graduate Center of the City University of New York, told The Chronicle that the decline may be a result of more rich people looking to giving modes outside of direct charity.

For example, Mark Zuckerberg and Priscilla Chan, who do not appear on the 2015 Philanthropy 50 list, last year pledged to give $45 billion to “improving this world for the next generation” through a limited-liability corporation.

(Check out Top 10 Most Generous U.S. Donors: 2015.)

The Chronicle reported some data that suggested mega-donations remained strong in 2015. The Philanthropy 50’s median donation in 2015 was $91 million, compared with $92.5 million in 2014.

Critics Weigh In

Zuckerberg and Chan’s decision to use of an LLC became a focus of criticism and brought more scrutiny of donors’ intentions at a time when Americans increasingly feel the economic system favors the rich and powerful.

The Chronicle said the 2015 Philanthropy 50 list would bolster arguments that ultra-high-net-worth people could do more good with their wealth.

It noted that the 23 Forbes billionaires among the top 50 donors gave less than 1% of their estimated wealth to charity in 2015, a total of some $3.6 billion.

It said this may indicate that many very rich Americans simply are not big donors, but added that other billionaires failed to make the list because they donate infrequently in huge amount or give anonymously.

Following are the 20 most generous donors on The Chronicle’s 2015 list.

J.B. Pritzker 

20. J.B. and M.K. Pritzker

Location: Chicago

Wealth source: Family, finance

Top cause: Social justice

Total giving: $101 million

Biggest gift: Northwestern University

 

19. Ruth Bedford (deceased)

Location: Westport, Connecticut

Wealth source: Family

Top cause: Medical care, human services

Total giving: $104 million

Biggest gifts: Norwalk Hospital, Westport Weston Family YMCA

Paul Allen (Photo: AP)

18. Ernest and Evelyn Rady

Location: La Jolla, California

Wealth source: Real estate

Top cause: Higher education

Total giving: $112 million

Biggest gifts: University of California at San Diego Rady School of Management, University of California at San Diego Jacobs Medical Center

 

17. Paul G. Allen

Location: Seattle

Wealth source: Technology

Top cause: Various

Total giving: $113 million

Biggest gifts: Arts and culture, brain and cell science, climate change, efforts to fight Ebola and wildlife conservation

 

Conrad T. Prebys 

15. Donald Sirkin (deceased)

Location: Seattle

Wealth source: Insurance

Top cause: Human services

Total giving: $125 million

Biggest gift: LightHouse for the Blind and Visually Impaired (San Francisco)

 

15. Conrad T. Prebys

Location: San Diego

Wealth source: Construction, real estate

Top cause: Medical research

Total giving: $125 million

Biggest gifts: Sanford Burnham Medical Research Institute, Indiana University at Bloomington, Public Broadcasting Service

John Arnold (Photo: AP) 

14. Louis Simpson and Kimberly Querrey

Location: Naples, Florida

Wealth source: Finance, insurance

Top cause: Higher education

Total giving: $137 million

Biggest gifts: Northwestern University, Princeton University 

 

13. John and Laura Arnold

Location: Houston

Wealth source: Finance

Top cause: Foundation

Total giving: $163 million

Biggest gift: Laura and John Arnold Foundation

Jay Faison

12. Jay Faison

Location: Charlotte, North Carolina

Wealth source: Technology

Top cause: Public affairs

Total giving: $166 million

Biggest gift: ClearPath Foundation (Charlotte)

 

11. Jack Taylor

Location: St. Louis

Wealth source: Retail

Top cause: Foundation

Total giving: $188 million

Biggest gift: Crawford Taylor Foundation

 

David Koch and his wife Julia. (Photo: AP) 

10. David Koch

Location: New York

Wealth source: Oil

Top cause: Medical care

Total giving: $192 million

Biggest gifts: Memorial Sloan Kettering Cancer Center, Deerfield Academy

 

8 (tie). Stephen and Christine Schwartzman

Location: New York

Wealth source: Finance

Top cause: Higher education

Total giving: $200 million

Biggest gifts: Yale University, Inner-City Scholarship Fund, John F. Kennedy Center for the Performing Arts

Alice Walton (Photo: AP)

8 (tie). David Geffen

Location: Beverly Hills, California

Wealth source: Entertainment

Top cause: Performing arts, education

Total giving: $200 million

Biggest gifts: Lincoln Center for the Performing Arts, UCLA

 

7. Alice Walton

Location: Millsap, Texas

Wealth source: Family

Top cause: Various

Total giving: $225 million

Biggest gifts: Various groups

 

Bill Gates and his wife, Melinda. (Photo: AP)

6. Bill and Melinda Gates

Location: Medina, Washington

Wealth source: Technology

Top cause: Foundation

Total giving: $272 million

Biggest gift: Bill & Melinda Gates Foundation (Seattle)

 

5. Pierre and Pam Omidyar

Location: Honolulu

Wealth source: Technology

Top cause: Various

Total giving: $327 million

Biggest gifts: Omidyar Network, Humanity United, Ulupono Initiative, HopeLab

Michael Bloomberg (Photo: AP)

4. John and Jenny Paulson

Location: New York

Wealth source: Finance

Top cause: Higher education

Total giving: $400 million

Biggest gift: Harvard University

 

3. Michael Bloomberg

Location: New York

Wealth source: Media and entertainment

Top cause: Various

Total giving: $510 million

Biggest gifts: Arts, education, environment, public-health groups and programs aimed at improving city governments around the world.

Richard Mellon Scaife (Photo: AP)

2. John Santikos (deceased)

Location: San Antonio

Wealth source: Real estate, entertainment

Top cause: Human services

Total giving: $605 million

Biggest gift: John L. Santikos Charitable Foundation at San Antonio Area Foundation

 

1. Richard Mellon Scaife (deceased)

Location: Pittsburgh

Wealth source: Family

Top cause: Foundation

Total giving: $759 million

Biggest gifts: Allegheny Foundation, Sarah Scaife Foundation

— Related on ThinkAdvisor: