For anyone who knows.
Basically, it seems to me like the technology in mobile GPUs is crazier than desktop/laptop GPUs. Desktop GPUs obviously can do things better graphically, but not by enough that it seems to need to be 100x bigger than a mobile GPU. And top end mobile GPUs actually perform quite admirably when it comes to graphics and power.
So, considering that, why are desktop GPUs so huge and power hungry in comparison to mobile GPUs?
I have the largest laptop GPU from the last generation; 3080Ti @ 16GB.
You must have very small fans moving a lot of air in a laptop. That means speed and speed is the primary cause of noise in fans. Larger desktop PC GPUs can have a larger heatmass sink and more/larger fans that run at a slower speed.
Aside from the noise, the laptop has a more complicated set of breakouts and interrupts for thermal and battery management. This means it may have different firmware/software support and issues if you do higher risk types of activities like messing with the clock rate.
One example I can give is when using AI on my laptop with various models I am able to split between CPU and GPU for inference. The thermal performance will impact throttling. I must balance both the workload and the thermals to maximize the inference speed for things like Low Rank Adaptors training where I need to run a model for a long time at near maximum output for my hardware. If there is more load on either, the shared thermal management will throttle sooner. Indeed I wrote a script to monitor the CPU/GPU temps and memory usage every few seconds just to dial in this issue.