Think back to the E36. People spent 20k+ more for their M's, and then a bunch of punks like us go and buy a few simple mods and make our POS 330's look just like an M3. (even if the more tasteful punks didn't re-badge)
Enthusiasts cried foul. M3's should look distinctive, not share the same body panels as the other 3-series cars.
I susepect the M-package for 3 series is not avaialble for reasons along these lines. BMW went back to the distinctive M3 with the E46 body style.
(Note: I own a 330, and no I don't think its a POS. But I have respect for th M3 owners... the M3 is one helluva fine automobile. They deserve to stay out.)