Well that's remarkably lame on Unity's part. Kind of what I suspected though.
Viewing post in Bug report
Yeah, I know right - Chewy may be able to tweak it for performance at some point once development has been completed, Unity cross-compiles content for Windows 32 and 64, Android and MacOS - he doesn't have a physical Mac to test on and uses a virtual machine - so the hardware getting hot wouldnt be something he'd be aware of.
I have a feeling it changed in Unity 2017 as I've seen a number of people talking about it being an issue since 2017 - Unity appears to have evolved to be more of a 3d game engine than the 2d it used to be.