I'm just guessing, randomly, but with some knowledge of wireless technology:

They may have switched the frequency of the wireless tire sensors to a more stable or secure platform or perhaps they coded them differently. At least, I'm assuming (guessing) they're coded to avoid the vehicle picking up the tire pressure from a vehicle next to it, etc.

Each year there are more and more interference sources, and frequencies issued. I'd assume that this is a piece of technology that BMW allows little room for error on, given the "potential" for liability on their end, should the TPMS system fail to indicate a loss of pressure.

If they were smart, they'd allow for backwards compatibility of older sensors. Again, from a liability standpoint, it would make the most sense for them to maintain compatibility with previous model year sensors.

But, again, I'm completely guessing and just adding my opinion to the mix. I'd assume a letter to BMWNA would confirm or repeal the above hypothesis.