Okay, let's look at your list.
Kills Years Name
17 1996 THOMAS HAMILTON
16 1987 Michael Ryan
12 2010 DERRICK BIRD
7 1999 RICHARD FIELDING
5 1986 GEORGE STEPHENSON
5 2003 Kenneth Regan & William Horncy
5 1985 Jeremy Bamber
So only THREE in double digits in the last 26 years.
So let's just look at the last year or so in the US.
Sixteen US Mass Shootings Happened in 2012, Leaving at Least 88 Dead | The Nation
February 22, 2012—Five people were killed in at a Korean health spa in Norcross, Georgia, when a man opened fire inside the facility in an act suspected to be related to domestic violence.
February 26, 2012—Multiple gunmen began firing into a nightclub crown in Jackson, Tennessee, killing one person and injuring 20 others.
February 27, 2012—Three students at Chardon High School in rural Ohio were killed when a classmate opened fire.
March 8, 2012—Two people were killed and seven wounded at a psychiatric hospital in Pittsburgh, Pennsylvania, when a gunman entered the hospital with two semiautomatic handguns and began firing.
March 31, 2012—A gunman opened fire on a crowd of mourners at a North Miami, Florida, funeral home, killing two people and injuring 12 others.
April 2, 2012—A 43-year-old former student at Oikos University in Oakland, California, walked into his former school and killed seven people, “execution-style.” Three people were wounded.
April 6, 2012—Two men went on a deadly shooting spree in Tulsa, Oklahoma, shooting black men at random in an apparently racially motivated attack. Three men died and two were wounded.
May 29, 2012—A man in Seattle, Washington, opened fire in a coffee shop and killed five people and then himself.
July 9, 2012—At a soccer tournament in Wilmington, Delaware, three people were killed, including a 16-year-old player and the event organizer, when multiple gunmen began firing shots, apparently targeting the organizer.
July 20, 2012—James Holmes enters a midnight screening of The Dark Knight Rises and opens fire with a semi-automatic weapon; twelve people are killed and fifty-eight are wounded.
August 5, 2012—A white supremacist and former Army veteran shot six people to death inside a Sikh temple in suburban Milwaukee, Wisconsin, before killing himself.
August 14, 2012—Three people were killed at Texas A&M University when a 35-year-old man went on a shooting rampage; one of the dead was a police officer.
September 27, 2012—A 36-year-old man who had just been laid off from Accent Signage Systems in Minneapolis, Minnesota, entered his former workplace and shot five people to death, and wounded three others before killing himself.
October 21, 2012—45-year-old Radcliffe Frankin Haughton shot three women to death, including his wife, Zina Haughton, and injured four others at a spa in Brookfield, Wisconsin, before killing himself.
December 11, 2012—A 22-year-old began shooting at random at a mall near Portland, Oregon, killing two people and then himself.
December 14, 2012—One man, and possibly more, murders a reported twenty-six people at an elementary school in Newtown, Connecticut, including twenty children, before killing himself.