Originally Posted by
parishiltons
Clearly you're not referring to practice in the USA.
More seriously, it's safety. Using ICAO standard phraseology gives a better chance of everyone understanding each other, including people who use English as a second or professional language.
Also with the increasing use of CPDLC, voice comms are gradually reducing and most datalink messages are preformatted to ICAO standard, with limited freetext.
When we were working on the initial message sets for CPDLC (South Pacific FANS1 1993-96) the most exciting part was that, at last, there would be a standard set of phraseology that could not be "tailored" for personal wishes. Of the four airlines involved (NZ, UA, QF and CX) guess which one voiced concern the the free text option was difficult to access.
Gne