Originally Posted by
chevvron
That's because most of the USA is Class E airspace where IFR flight is mandatory and hence an individual code is allocated..
IFR isn't mandatory it's mixed IFR/ VFR ( that's why it is recommended to continue the "see and avoid policy).
Now the purpose of class E is, at certain minimums, to have everyone on IFR below those minimums.
I forgot to say but, 1200 is the VFR squawk