I have zero ideas, I just assumed it was because I went to a bargain bin place to mount my wheels. I told them to just put the old TPMS to the new wheels and they didn't even know what that was. I just got it reset for free from my Nissan dealership during my oil change.
That's weird. My SLs came with 3 tires and regular valve stems so I drove around with those for like 6 months but when I got new tires I had the shop(Firestone) put my TPMS on my SLs. No problem. :shrug:
Another reason could be if they aren't put back in the same wheels the signal can be thrown off, there's a bunch of things that could happen with those stupid sensors. I had the guy do everything in front of me and have them put back in the exact same spots and had him use the TPMS rebuild kit that was offered with my rims and my light stayed off.