So here's what I am thinking in my 18 year old head:
There hasn't been a single train carrying a GM product on that part of the Lake Orion Branch in more than a decade... The last train that ran on that line iirc was the RBBB circus train in like 2017 or something like that, I guess CN kept the line after GM stopped shipping because RBBB must've been paying A LOT of money, and when I mean a lot, well, here's my guess, After GM stopped shipping cars out, assuming the RBBB only did 1 show per year at the palace, there were only 2 trains per year, count 1 run in and 1 run out, therefore you get two trains per year. I don't think CN would've kept the tracks in unless they were being paid to keep it (and the crossings) in operating condition, and even before the tracks were cut, there were rumors going around that CN was going to take up the tracks even before the RBBB shut down.
The one caveat was the RBBB using the line, which would make me think they (RBBB) were paying CN money to maintain everything, and that was probably a pretty significant sum. It almost seems like the RBBB was the only thing that was keeping that part of the line in use, because right after the (no pun intended) curtain closed on the RBBB, CN almost immediately cut the tracks at Collier, which would make me think that GM didn't want it to return to service in the first place.
If they hadn't cut the tracks at Collier, that would've been a sign that GM was, at one point, paying CN to save the line for later. However, as everyone knows, it's been cut, which would make me think that GM doesn't want it for future use, but as I believe DaveO pointed out in an older post, CN is only keeping the line in a non-abandoned/out-of-service state for tax purposes. If they (CN) got those tax incentives taken away, I would bet my entire scaletrains.com locomotive collection that those tracks would be gone within months, and that's a lot to bet .
Just a few ideas, probably makes no sense but I felt like it could be of some importance.