Bronco Billy1980 · Film · 116 minDirected by Clint EastwoodDramaRomanceComedyAn idealistic, modern-day cowboy struggles to keep his Wild West show afloat in the face of hard luck and waning interest.1 neutralfrom 1 commenter♥ Like＋ Watch laterIMDbTMDBTrendsWhere to watchNo streaming data for this title.
Hacker Cinema
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Looks to be a different source from the OP, but let's go down the chart for 1980 past the top ten:
https://www.boxofficemojo.com/year/1980/
Kramer vs. Kramer (book)
Ordinary People (book)
Popeye (comic)
The Shining (book)
Cheech and Chong's Next Movie (sequel)
Caddyshack (original - franchise starter)
Friday the 13th (original - franchise starter)
Brubaker (book)
The Jazz Singer (remake)
Flash Gordon (sequel/remake)
Bronco Billy (original)
Raging Bull (book - biopic)
Maybe you should go back a few decades until you can find a time when the top 20 were mostly originals. Would have to be before the Star Wars/Jaws blockbuster era, probably.