[noggin]

I think that's down to Amazon and Netflix.

They both automatically change refresh rate on other platforms such as the Amazon Fire TV.  

 No - they don't automatically change refresh rate on Amazon Fire TV.  AIUI Amazon Fire TV OS apps still have to be enabled to do this, just as I believe Android apps do.

I've just checked - my Fire TV Stick 4K automatically switches from 59.94Hz to 23.976Hz or 25Hz output in Amazon Prime Video.   In Netflix and BBC iPlayer it stays at 59.94Hz whatever content I play (iPlayer is 50Hz, Netflix is a mix)