This goes back to the Netscape / SUN partnership. SUN allowed Netscape to use their trademarked name Java when they created JavaScript. Microsoft created JScript. When they decided to standardize the language into a spec, they did so with ECMA. The involved parties couldn't agree on a name so they settled on the highly original name ECMAScript as a compromise.

"Eich commented that "ECMAScript was always an unwanted trade name that sounds like a skin disease.""

And, just to round this out, SUN is all-caps (rarely) because it was originally an acronym for Stanford University Network.

TIL and can now go to sleep