1) Heated metal expands, and different heated metals expand at different rates, changing tolerances for threaded mounts and possibly causing thermal locking and/or looseness.
2) Managing heat over time is about diffusing the dangerously high temps (e.g. near boiling) to areas large enough stay safe for human contact while also being exposed to air to shed that heat. A pinch point threaded mount under a rubberized/plastic body will absorb thermal shocks (quick use) but will equalize to very close to the junction temperature of the processor over time, aided only slightly by the other parts of the camera that are poor thermal conductors. Basically, that spot would become a burn risk.
See ASTM C1055 - https://www.astm.org/Standards/C1055.htm
The short version is that you need to keep things under 60C/140F if there's a chance a person could touch it.