not a mistake
The mcu2 needs new digital tuner instead of analog one in mcu1 cars.
And that replacement is a lot of labor, so somebody run the numbers and decided that it's good enough as is.
I don't blame tesla for excluding the new tuner (am/fm/Xm for mcu2). I put one in my car in my recent mcu2 retrofit and the tuner was the hardest part by far. Took like 2 hours and was awkward as heck. The bolts are very hard to get to behind the steering column. Tesla made the right choice for retrofits.