But Why Not (foaled in 1944) was an American Thoroughbred racehorse. The daughter of Blue Larkspur and granddaughter of Black Servant is probably best remembered for wins in the Alabama Stakes, the Acorn Stakes, the Black-Eyed Susan Stakes at Pimlico Race Course. In 1947, she was voted by the country's top sports writers as the American Champion Three-Year-Old Filly. Three-year-old season But Why Not did not run as a two-year-old. In 1947, she ran in eleven races over ten months and won most of them. After breaking her maiden and winning an allowance race, she ran in the Empire City Stakes in early April at the old Jamaica Race Course in New York, where she placed second to Phalanx at 9.5 furlongs. She rested for six weeks and then competed in the $25,000 Black-Eyed Susan Stakes (then called the Pimlico Oaks) on May 16, 1947. The race was held at Pimlico Race Course in Baltimore, Maryland, and was run over a distance of one mile and a sixteenth on a fast dirt track. In that race, But Why Not beat stakes winners Cosmic Missile and Oberod in a time of 1:46.40 under jockey Warren Mehrtens. Later that year, But Why Not reeled off five victories in seven stakes races. In the beginning of June, she won the Acorn Stakes at Belmont Park. Then she shipped to Chicago, Illinois, in late June and won the Arlington Classic at a mile in open company on the turf. She added another win that year at Arlington Park in the Arlington Matron Handicap at a mile on the dirt. In August, But Why Not traveled to upstate New York and ran in the prestigious Alabama Stakes at Saratoga Race Course. In that race, she beat Miss Grillo going away in 2:05 flat over a mile and a quarter on the dirt. She also finished second in the Dwyer Stakes against males, losing again to Phalanx, and second in the Ladies Handicap to Snow Goose at Belmont Park Four- and five-year-old seasons Early in 1949 at Jamaica Race Course, But Why Not raced against fillies and placed second behind Lithe in the Comely Stakes. Then her owners at King Ranch entered her in the Metropolitan Handicap at Belmont Park over the Memorial Day weekend. But Why Not finished third to Loser Weeper and Vulcan's Forge. She again took on males on the Belmont Stakes undercard