Variety tells us:
A record 92 animated short films have qualified for the 92nd Academy Awards, a list that will be winnowed to 10 contenders when shortlist is announced Dec. 16. Alongside entries such as Sony’s “Hair Love” and Magic Light Pictures’ “Zog,” challengers include lauded films from animators such as Tomek Popakul’s “Acid Rain,” Siqi Song’s “Sister” and Theodore Ushev’s “The Physics of Sorrow.” Ranging from studio darlings to festival gems, the diversity of projects in the category makes for a somewhat unpredictable race. ...
Walt Disney Productions stopped making shorts in 1958 or thereabouts. M-G-M stopped making new shorts in 1957 when it closed its animation department and set Bill Hanna and Joe Barbera adrift. (SPOILER ALERT: they started their own company the same year and ended up doing rather well.)
Warner Bros. Animation -- which concentrated on shorts -- limped along until 1963, when that studio breathed its last. (Of course, nothing is forever. Warner Bros. Animation started up again in a limited way in the 1970s, finally expanding in a way way in 1989 when it partnered with Steven Spielberg for Timy Toons, then launched other animated series.)
Walter Lantz, working under the Universal umbrella, made increasingly anemic theatrical shorts until 1972, and then gave up the seven-minute cartoon biz. Friz Freleng and Dave DePatie made Pink Panther theatrical shorts alongside dtelevision product until 1980. But for the most part, theatrical shorts in the latter part of the 20th century were as extinct as the T-Rex.
But that dynamic has changed. Shorts, lots of shorts, are being made again. The problem now is getting them shown in regular theaters with regular, main-stream live-action features. That's the final frontier.