You're right in that it doesn't HAVE to, but it is. And it isn't going to change. Radio traffic in the U.S., for the most part, is from native English speakers, all from the same airlines going all over the country. And they all know and use the same idioms. That's the way they talk, everywhere, and nothing will change it. New guys listens to it, and start to talk that way themselves.
In Europe, all the non-native English speakers speak various proficiencies of English on aviation radios in all sorts of accents, so everyone has to stick to the script, just to be understood. Now, if every state in the U.S. had a different language, and their pilots learned English specifically to speak on the radios, THEN it would be like Europe over here.
There's the difference.
Bubba
Maybe one day... or at least we can hope.
https://www.faa.gov/nextgen/update/progress_and_plans/data_comm/
"Voice communication is labor intensive, time consuming and limits the ability of the National Airspace System (NAS) to meet future traffic demand. The use of Data Comm will lead to increases in NAS capacity and a reduction in flight delays. Data Comm will also enhance safety by reducing operational errors associated with voice communications, such as misunderstood clearances and instructions."