The most successful push on spelling was when the Chicago Tribune switched to simplified spelling in the 1940s through the 1960s.[1]
They started with about 40 words, and gradually expanded. But after McCormick died, the company gave up, retaining only "tho" for "though". That ended in 1975.[2]
[1] https://www.spellingsociety.org/uploaded_media/tribune-media...
[2] https://www.nytimes.com/1975/09/30/archives/thru-is-through-...