To add to this there was discussion on the SL discord on this topic. The idea behind that reflection probes are meant for the environment, not for an avatar/person. While I still think not allowing attached reflection probes to an avatar still shouldnt be allowed to follow in that step. I do think allowing attached reflection probes to root prims should still be allowed and there is several use cases of it needing to be in the world of SL.

1st: Many building/environment rezzers will rez items then move objects into location after rez. This is used for rezzing houses and also games like GoThongs where items get rezzed and moved by scripts and having probes attached so they moved with the environment that is being moved on rez is respected.

2nd: Another use case I ran into is what to do about boats. While it can be argued that a small dingy/row boat doesnt it own probe. Larger boats like yachts/cruise ships and such ARE their own environments with their own rooms just like any building but they also just so happen to move. Needing to allow probes be attached to the root prim is critical for this to function with no other method would cover for this. Since there would be no good way for auto probes to cover these cases and I doubt we will see areas like the blake sea be manually probed. See screenshot of what is essentially a building room that should have its own probe (but it also moves because its a boat)

There is also precedence for this in the gaming industry such as BeamNG that uses a hero probe that follows the car through the world. It is also mentioned here https://feedback.secondlife.com/feature-requests/p/llvehicle-hero-probes